MSL "Heat shield woes" Options

[Stu]

"MSL Heat Shield Woes" - Aviation Week

Anyone else see this?

[centsworth_II]

From the article:
"The relative orbital positions of the Earth and Mars allow for a shorter
trip time in 2011, although the spacecraft will hit Mars' atmosphere at a
higher velocity, which has implications for the TPS..."

Maybe this is naive, but can't they control the velocity with which
MSL hits Mars by reducing the boost it gets at the beginning of its
journey and lengthening the trip time?

[djellison]

Do that, and you don't reach Mars at all. The journey time ( and arrival speed ) are dictated by the trajectory which is dictated by the orbital mechanics.

Doug

[centsworth_II]

I bet Dawn wouldn't have any trouble.

[nprev]

Not to be cynical, but 'pray for launch delay' is a very common mantra in some circumstances for many programs (mostly those confined to Earth orbit)...

[mchan]

The delay for MSL would be 2 years and very costly. Doubt there are many prayers for a delay in this particular case.

The 2011 launch date is the faster trajectory, so launching in 2009 would avoid the problem.


This post has been edited by mchan: Feb 18 2008, 08:10 AM

[AndyG]

Is the article correct?

NASA had planned to use a super lightweight ablative (SLA) heat shield for MSL, similar to what is used on the space shuttle's external tank

I thought the SLA for ablative re-entry use was nothing like that used on the tank? Am I wrong?

Andy

[rlorenz]

Do that, and you don't reach Mars at all. The journey time ( and arrival speed ) are dictated by the trajectory which is dictated by the orbital mechanics.

Yes - sort of.

The launch date, launch speed, arrival date, arrival speed and arrival location are all coupled. Not all
points in this five-dimensional space are populated for a given launch vehicle, and some points are
not populated at all.

For a given launch vehicle, clearly you can only attain some utter maximum speed, and below that
the launcher has a mass/speed performance envelope. The launch speed dictates the relationship
between launch and arrival dates, and arrival speeds.

Specify some other parameters (like launch speed) and you introduce a coupling between arrival
date and/or speed and location. It might be possible to tune the trajectory to a lower entry speed,
but not if you force the landing site to be in a particular place.

Thus it might be that you could 'take the slow road' to Mars, but maybe not to get exactly where
you want to.

I think Doug meant all of the above, but was just saying 'orbital mechanics' as shorthand... ;-)

[djellison]

Yeah...I meant every word of that...all of it.

Easy solution - read the first 20 pages of


Planetary Landers and Entry Probes

For more R.L. et.al goodness on such matters.

That's what I've been doing over the weekend. I'll need to read it twice for it to go in, but at least I know what b-plane means now.

Doug

[ElkGroveDan]

Ouch $115...but you can get a used one on Amazon for $105 .

Why can't you rocket scientists write in popular paperback? Also if you throw in a murder mystery and a love scene between discussions of thruster vectors, we can convince our other-halves that it's a worthwhile purchase.

[Greg Hullender]

Part of what I love about orbital mechanics problems is that they're so rich. In this case, although there's certainly a unique minimum-energy transfer orbit (which also has minimum arrival velocity) at any given launch window, there's a vast abundance of higher energy and higher arrival-speed orbits. That's true even if you insist on the transfer orbit being smoothly tangent to the orbit of Mars (as opposed to simply smashing straight into it from the side.) Also, since Mars has a highly elliptical orbit, even minimum-energy orbits will vary from one launch window to the next, with lower energy (and thus lower arrival velocity) when Mars is closer to the sun at arrival time.

Moral: You can get to Mars faster than a Hohmann orbit, but you'll be going faster when you get there.

--Greg

[edstrick]

Mariners 6 and 7 <1969> had unusually short trip times to Mars, something like 5 months. They were launched as second generation Mariners on Atlas Centaur rockets instead of the Atlas Agena that launched the early Mariners and Rangers. Launch vehicle had more or less the same capability as the one that launched Mariner 9 to orbit Mars on the next opportunity, BIG fuel tanks and all. Mariner 69 were flybys and a little ?more? than half the weight of Mariner 9, so the launches had energy to spare. They were kicked into fast flybys, that also had a mission irrelevant gravity assist that kicked the aphelion out to the edge of the inner belt. Had the record as the furthest solar powered spacecraft from the sun till NEAR, Stardust, or perhaps Rosetta got further out at aphelion.

You would NOT have wanted to retro into Mars orbit from those encounters. The "Hyperbolic excess velocity" -- very useful term in these discussions, the speed the spacecraft approaches and receeds from the planet at effectively infinity (ignoring the sun) -- was much larger than for an orbit insertion bound mission.

[Guest_Sunspot_*]

Is MSL really going to be ready to launch on time?

[djellison]

To be honest, compared to the trouble MER had, MSL's got it easy.

Doug

[elakdawalla]

Alan just said at MEPAG that, just three months after the Herculean efforts to solve the last budget overrun (which was $62M), MSL has come to HQ to request another $165 to $200 million.

--Emily

[djellison]

Oh dear. That's really very very bad news indeed.

[centsworth_II]

Wouldn't it be ironic if MSL doesn't fly and ExoMars does?

[ugordan]

Ironic, indeed. I don't think Alan will like that request one bit.

[djellison]

I really really really want to see MSL fly, but it pains me to say, Alan's in a situation where a painful decision may have to be taken.

[elakdawalla]

Alan went on to say "The ramifications are going to be severe in the science division, but we are supporting MSL." He also said that the cost of delay to a 2010 or 2011 launch would be an additional $200M.

--Emily

[Guest_Sunspot_*]

Alan went on to say "The ramifications are going to be severe in the science division, but we are supporting MSL.
--Emily

It's pointless sending it if it's to be stripped of most of it's scientific capability. It's hardly more than a long range MER even. now.

[vjkane]

Emily -

Are you at the MPEG meeting?

[elakdawalla]

No. They're trying out allowing people to participate via WebEx -- you can see the slides on screen and call a toll-free number to hear the audio. I'm probably not going to tune in to much more of it today.

--Emily

[Mariner9]

I hate to be an armchair quarterback, so I'm not going to say even one tenth of the things that are running through my mind right now.

The cost overruns on MSL have already dug holes in other people's budgets, and it just keeps right on gobbling up money.

I admire the incredible things JPL has accomplished in the last 40 years, including the spectaculare sucess of the Mars Exploration Program, but JPL has allowed an 800 million dollar project to baloon into a 1.8 billion dollar project. And all of this after the hard lessons of Mars 98 were supposed to have instilled a sense of reality into project planning.


By the time this whole mess gets sorted out it will have done a lot of damage. I shudder to think what might end up happening to the Mars program. The Fiscal 2009 budget cuts may be just the begining.

[elakdawalla]

One of the things that makes me a bit worried is that the Mars program might wind up eating other programs. For instance, Alan pointed out that priority given to Phoenix' launch imposed a $40 million charge to the Discovery program because of the delay of the Dawn launch, and he also brought up the possibility of opening up the New Frontiers line to Mars missions. The next New Frontiers mission will have to be inner solar system, no further out than Jupiter, because there's not enough plutonium left (he said) for anything in the outer solar system -- it'll have to be solar powered. There's already seven spacecraft scheduled to go to the Moon. That leaves small bodies and Venus in the original New Frontiers manifest. If they open it up to Mars, I wonder if that means New Frontiers will necessarily wind up at Mars because the risk of such a mission would definitely be lower than for a Venus mission.

--Emily

[ugordan]

One of the things that makes me a bit worried is that the Mars program might wind up eating other programs.

I'm probably overly pessimistic, but what are the chances of this affecting the next outer planet flagship?

[elakdawalla]

I have no data with which to back this up, but my instinct is that as long as Alan is in charge, an outer planets flagship will move forward.

--Emily

[rlorenz]

Ouch $115...but you can get a used one on Amazon for $105 .

Why can't you rocket scientists write in popular paperback? Also if you throw in a murder mystery and a love scene between discussions of thruster vectors, we can convince our other-halves that it's a worthwhile purchase.

I sympathize.

But this remark betrays a sad ignorance of the publishing industry. The rocket scientist authors have
exactly ZERO say in specifying the print run of the book or its sales price.

My experience with several different publishers (CUP on Lifting Titan's Veil and Planetary Landers;
Springer/Copernicus on Spinning Flight, Springer/Praxis on Space Systems Failures and Princeton
on Titan Unveiled) varies slightly in detail, but all
- take longer to publish than you want
- promote the book less than you want
- sell it at a higher price than you want

Planetary Landers is frustrating in that CUP have clearly priced it as a text, putting it out of the budget
of the space enthusiast.
Titan Unveiled, happily, looks like PUP has priced it to shift...

[djellison]

One thing that I think Jim Bell was pushing for with a book of his was an e-book version for a not-crazy fee. Obviously, publishers are publishers, and the little exposure I've had - they are a law unto themselves doing everything that seems illogical to both author and reader.

[Jim from NSF.com]

There's already seven spacecraft scheduled to go to the Moon. T

You mean proposed. There is only one mission past confirmation at this point

[djellison]

Chang'e 1, Chandrayaan - 1, Kaguya, LRO. That's four ( or, if you want to get picky, six given the Kaguya sub-sats)

LCROSS, that makes 5. Grail - that's 6 and 7 (or, again, 8 and 9 if you count the Kag-sub's). Taking Chang'e 1, Chandrayaan 1, Kaguya, LRO, LCROSS and 2x Grail - there's your 7.

No one said that Alan was talking about 7 NASA spacecraft going to the Moon.

[Jim from NSF.com]

point taken

[mcaplinger]

...JPL has allowed an 800 million dollar project to baloon into a 1.8 billion dollar project.

Out of curiosity, where do you get the $800M and $1.8B numbers?

[Mariner9]

The 800 million figure was rather informal. I was at a JPL open house 4 or 5 years ago and had a chance to speak to one of the engineers on the project. I asked him about the estimated cost, and he said that they felt it would be no more expensive than MER. I was rather dubious about it, but he said that since there would be only one MSL, as opposed to two MERs, that the cost savings in only a single launch, flight operations, etc, should help contain the costs and it would not be any more expensive than the MER project.

Uh, huh.

Admitedly this was a very un-official conversation. But he made it sound like this was the internal consensus at the time. Right off the bat it occured to me that an Atlas V launch costs a heck of a lot more than a Delta II, so this didn't look like a very realistic expectation on their part. I had this very bad feeling that JPL was being too optimistic in their cost estimates, and overly ambitious on the project technical challenges.

Later I remember seeing numbers that kept climbing with every report, such as like 1.2 billion and 1.5 billion in Aviation Week. A few months ago when the third cost overrun was reported (and Alan Stern made them scale back some of the instruments) the figure had crept up to 1.7 billion.

If additional problems recently identified adds another 1-200 million, that takes the project cost as high as 1.9 billion.... so I thought it reasonable to throw out a ballpark figure of 1.8.

I'm not going to say "I told you so" because I've never built a MARS rover personally, but that bad feeling I had at the time seems to have come true.

[mcaplinger]

The 800 million figure was rather informal....
Later I remember seeing numbers that kept climbing with every report, such as like 1.2 billion and 1.5 billion in Aviation Week. A few months ago when the third cost overrun was reported (and Alan Stern made them scale back some of the instruments) the figure had crept up to 1.7 billion.

You'll forgive me if I call BS on this. A hallway conversation with somebody at a JPL open house? Media reporting? Are those figures with or without margin and reserves? Are they in real-year dollars? Do they include the launch vehicle? How about the RTG? How about foreign contributions? Is this through the end of the mission? What are the ops cost assumptions?

If you're going to condemn the whole project on the basis of cost overruns, you might want to really understand what the initial cost estimates were, what has actually been spent, and what is further costs are expected and authorized.

[mchan]

The next New Frontiers mission will have to be inner solar system, no further out than Jupiter, because there's not enough plutonium left (he said) for anything in the outer solar system -- it'll have to be solar powered.

You had blogged a story on nuclear-powered Discovery mission using the ASRG in which Alan Stern stated that he would not risk a new power supply on a flagship without seeing it run successfully on a cheaper mission first. Well, a New Frontiers mission is cheaper than a flagship, and there is evidently enough plutonium to run the ASRG.

The likely answer is that the longer time of flight of an outer planets New Frontiers mission has a higher risk of long-life failure from the ASRG than a shorter time of flight of an inner planets Discovery mission.

[Mariner9]

You'll forgive me if I call BS on this. A hallway conversation with somebody at a JPL open house? Media reporting? Are those figures with or without margin and reserves? Are they in real-year dollars? Do they include the launch vehicle? How about the RTG? How about foreign contributions? Is this through the end of the mission? What are the ops cost assumptions?

If you're going to condemn the whole project on the basis of cost overruns, you might want to really understand what the initial cost estimates were, what has actually been spent, and what is further costs are expected and authorized.

I don't really appreciate your flame. Someone asked where I came up with the 800 million, and I honestly replied it was an informal number given to me in a non-official setting. As for "include the launch vehicle?" ... yes, it was a number that was supposed to reflect total project costs.

As for "media reporting"..... Aviation Week is one of the most respected aerospace journals out there. Is it always dead on? No, but it used to be nicknamed "Aviation Leak", and foreign govenrments routinely used it as a source for intelligence gathering.

Last fall Alan Stern stated that JPL had come to headquarters with three different cost overruns. This latest one would be at least the fourth.

If you are going to slam me, then I would ask you to provide me with your source of information that there have not been serious cost overruns on MSL. Because my supposedly "BS" sources have turned out to be remarkably accurate from what I can see.

[mcaplinger]

If you are going to slam me, then I would ask you to provide me with your source of information that there have not been serious cost overruns on MSL.

How about the annual NASA budgets from the beginning of the MSL project to now? It's a matter of public record how much has been spent to date.

[Mariner9]

NASA budgets are a matter of public record. That is indeed true. But making that statement is hardly what I would call a cost analysis.

Going back to Alan Stern stating that there had been three separate cost overruns on the MSL project, was he lying when he said it? Perhaps you could provide us with a year by year breakdown of the budget and show us all that Mr. Stern was completely mistaken.

[stevesliva]

Wasn't there surprise that the Mars budget was decreased a bit in the last NASA budget?
Does that mean that this was anticipated? Do the real numbers that result from this mean that there is effectively no decrease?

Did the budget reflect a number that was "what you wouldve gotten minus what you're going to need for MSL overruns?"

[mcaplinger]

NASA budgets are a matter of public record. That is indeed true. But making that statement is hardly what I would call a cost analysis.

No, but since I'm kinda busy building instruments for MSL, I assumed you might take the time to look at them yourself.

Rather than debate this, though, I suggest you read pages Sci-153 through Sci-158 in the in the FY09 budget. On page Sci-156, we see that the current total development cost estimate for MSL is $1.035B, increased by $66.4M from the base year (2007) estimate. The total cost of $1.66B shown on Sci-153 includes formulation and operations costs. One would have to look at previous year budgets to assess how much this has increased, but I find it hard to believe that the mission ever cost the claimed $800M in an apples-to-apples comparison; budgets are all online at http://www.nasa.gov/news/budget/index.html

[Mariner9]

More power to you for unraveling those budget documents (seriously). I started reading through them and it drove me crazy trying to find the same summary information working backwards through the years, since the format changes from year to year.

So assuming that the 800 number was just something tossed out informally by someone who was not reading a budget projection at the time (which is what I've said all along anyway) ..... so.... uh....

Well, I stand corrected. Obviously the MSL project is not suffering a series of cost overruns. Alan Stern must have been mistaken when he claimed that multiple budget overruns have crossed his desk. All those articles in the press must have got it all wrong. And these latest reports of another overrun with the potential for tens of millions (I think up to 200 million was mentioned more than once) ..... must just be rumors.

Glad that we got that settled.

[elakdawalla]

Boys, boys, can we please take it down a notch? You're both understandably frustrated -- Mike because there's a history of blame games and finger-pointing in who's responsible for the overruns, some of which was unfairly laid at the feet of the instrument teams, and Mariner9 because of an instinctive worry that MSL is becoming The Mission That Ate The Mars Program and the feeling that the overruns are out of control. I'll second the remark that figuring out where the overruns are coming from is fiendishly complicated; at TPS during all the mayhem last fall we tried to gather information from multiple sources on who was running how much over budget and why and whose fault it was and in the end we couldn't get enough pieces to make it all add together. Yelling at each other in this thread isn't going to solve anything.

--Emily

[Mariner9]

Sorry, I almost posted a retraction (or a partial one anyway) right after the last post, but you beat me to the punch.

Yeah, I'm worried that the overruns will affect other projects. I'm sorry if anyone thought I was being holier than thou or pointing fingers. In fact, I have no idea what technical or program reasons have caused the specific overruns MSL has experienced, and I'm always impressed that any of these missions suceed in overcoming both the technical and bureaucractic hurtles thrown in their ways.

I'm under no illusions that this stuff is easy. I'm in the software industry, and god help any spacecraft that would get loaded with software that my group had anything to do with.......

[vjkane]

Emily, did Stern have anything to say on why the Mars budget was cut so much? I presume it was to fund all the other new starts (not a bad trade off in my opinion). But I'd be interested in the official explanation.

Also hoping there will be one of your excellent blog entries on what was said.

[hendric]

I can see it, but I'm not sure I can make anything intelligible out of it:


Based on the years in common, it looks like it went up from 956 (FY2007-2011 in FY07) to 1069.2 million. However, the better comparison is probably 07 and 08 predicted budget in 2007 vs actual budget reported in 2009, where it went from 632.5 to 722.3 million, or growing by 14%.

[Steve G]

NASA is always reinventing the wheel. Every spacecraft for Mars is a new and expensive design. MSL has a brand new landing concept, and that's just the beginning. Would it not be prudent for NASA to say, okay, here is the design we'll be using for the next decade. So rather than moving towards a sample return mission, (more billions) just build four of five addional MSL's over the next fifteen years and make it the cornerstone of your Mars exploration strategy? I don't expect assembly line econiomics, but certainly the cost of the sixth spacecraft will be a lot less than the first. We have also learned from the MERs that Solar Panels are feasible for long duration missions, simply have a cleaning and better pointing mechanisms for them and you won't have to worry about pluotonium production shortfalls and save them for outter planet missions.

[djellison]

Every spacecraft for Mars is a new and expensive design.

MER was Pathfinder heritage. Odyssey was MCO heritage. Phoenix is MPL heritage. I can see the point you're trying to make, but it's not entirely true. The one major problem - we can barely afford one MSL. Where is the money to build several more? There isn't any. More often than not, you want to fly a specific payload, and that specific payload has specific accommodation requirements and landing site challenges and thus requires a unique solution. I'm sure, if successful, the MSl decent profile will be re-flown several times in the future, but there isn't the money to fly many MSL sized vehicles, nor are there many interesting places where you could safely send MER clones.

Doug

[brellis]

NASA doesn't want to waste a lot of $$ in new R&D, so even if a design is technically 'new', it's not a complete reinvention of the wheel.
Innocent opinion: MSL looks like a big MER; they didn't start entirely from scratch. Also, some new landing methods are the result of investments in R&D from years past. Why not enjoy the fruits of that labor?

That said, I really wish we could make several copies of successful rovers and spacecraft. It would be great to have several Cassini's and several MER's/MSL's. Maybe they find gold on Mars and Titan, and private investors will pony up!

[vjkane]

That said, I really wish we could make several copies of successful rovers and spacecraft. It would be great to have several Cassini's and several MER's/MSL's. Maybe they find gold on Mars and Titan, and private investors will pony up!

Proposals for series of missions have been made in the past. Cassini was originally supposed to be the first mission using the Mariner Mark II series to explore comets and the outer planets. The problem has been to secure follow on funding for the subsequent missions.

[brellis]

Right, I forgot about Mariner Mark II. If only NASA's budget were double its current size, think how many replicas would be moving through production at reduced cost.

Regarding private investment, I wonder if a really longterm partnership with private investment funds could be formed where sample return leads to mining, and manned missions lead to tourism. Are there enough billions out there to do it without draining the global economy?

If I had the choice, I'd rather dedicate my 401(k) to the space program.

[edstrick]

"...Cassini was originally supposed to be the first mission using the Mariner Mark II series ..."

JPL Director Bruce Murray <I think> had a major article in Science magazine in the mid 80's explaining in detail how the newly concieved Mariner Mark II program would provide the basis for continuing low cost planetary exploration. Mission costs <I think> were to be well sub-1-Billion-$, achieved in part by reusing modifications on a common spacecraft bus, much the way Mariners 69, 71, 73 and Viking Orbiters had massive design heritage.

The first missions were to be Comet Rendezvous / Asteroid Flyby CRAF and Cassini.

Well.... as the mission pair cost past umpteen billion, CRAF was nuked and Cassini was descoped to (among other things) a No-Scan-Platform mission.

"The road to hell is paved with good intentions"

I'd really like to see the story of how Mariner Mark II went form good intentions to budget control hell. Watching MSL, I'm getting massive deja vu.

[vjkane]

The pre-MRO Mars orbiters, as I understand it, shared much of their designs, which helped kept costs down. One idea I have would be if NASA were to design a new platform capable of orbiting Venus, the moon, or Mars (there are some thermal problems, but as Venus Express and several studies have shown, it is possible) and then hold a Discovery-like competition to pick the target and payload for a new mission every two years. I think we could get some really nice missions out of that at a fairly low cost.

Alternately, NASA could complete its just announced partnership to develop cheaper and more capable radar systems and then fly a copy at Mars and Venus to study both the surface and sub-surface.

There are lots of ways to do good science and lower costs. But this approach requires planning a series of missions and amortizing development costs.

[nprev]

This is the third or fourth time I've seen mass production of planetary spacecraft come up on the forum (I instigated one such discussion). Unfortunately, in order to realize any economy of scale, you not only have to place severe constraints on payload mass & volume that may well severely restrict the type of experiments that can be flown, but you also have to assume a stable budget environment for many years...and historically, the latter has been anything but. The third fly in the soup is technological advancement, which tends to obviate long-term configuration control as new methods become available.

[mcaplinger]

I'd really like to see the story of how Mariner Mark II went form good intentions to budget control hell.

One big reason is that the Cassini and CRAF missions were not really very similar, so the idea of sharing a common spacecraft was not that valid to start with.

As I have pointed out before when these "common spacecraft" discussions come up, there is huge commonality at the box level. Regardless of how different spacecraft may look on the outside, much of the guts are built out of catalog items.

[tedstryk]

There was also the problem of NASA's budget not being able to support Mariner Mark II missions at a rate that would make the "assembly line" advantage practical.

[Mariner9]

One example of design inheritance working well was Rosetta - Mars Express - Venus Express.



Venus express was a nearly identical ship to Mar Express, with almost the same collection of instruments. In fact, the ESA leaders put out the request for proposals of what kind of mission could be flown with the Mars Express vehicle, and do it shortly after Mar Express so they could keep the same engineering teams together to do the work. Thus, Venus Express was born.

Venus Express flew, the cost for that mission was far, far lower than a comparable NASA planetary mission. However, it was limited to be a near repeat of Mars Express, just flown to a different destination. And then mostly with instruments originally selected for a comet mission 10 years earlier.

Typically scientists and engineers identify a mission they want to fly, then design a spacecraft around those requirements. That isn't what happened in this case.

Venus Express was not a mission in search of a spacecraft. It was a spacecraft in search of a mission.

So there is a real downside on "assembly line" spacecraft . You are very limited in how you move forward.

A big part of MSL's problems may have been avoided if they had stuck to a modestly scaled up MER. However, MER was already pushing the size and weight envelope of the airbag delivery system. So you would have been stuck flying another MER, and never get anywhere near to MSL's capabilities. I've expressed a lot of concerns over the MSL cost problems, but I completely understand that in order to move past MER that the engineers had to take some risks.

[Tom Tamlyn]

>Venus Express flew, the cost for that mission was far, far lower than a comparable NASA planetary mission

One interesting aspect of the cost efficiencies of Venus Express is that they depended to a large extent on assembling the spacecraft immediately after (or indeed, concurrently with) Mars Express. If I recall correctly, a fascinating ESA discussion (can't remember source) said that even a several year delay would have largely vitiated the cost savings of the twin mission approach, due to the ordinary obsolescence of contractor tooling, processes, and parts used in fabrication.

TTT (Heraclitus said as much several millenia ago)

[vjkane]

One interesting aspect of the cost efficiencies of Venus Express is that they depended to a large extent on assembling the spacecraft immediately after (or indeed, concurrently with) Mars Express. If I recall correctly, a fascinating ESA discussion (can't remember source) said that even a several year delay would have largely vitiated the cost savings of the twin mission approach, due to the ordinary obsolescence of contractor tooling, processes, and parts used in fabrication.

When NASA was considering series of missions, it was always pointed out that a key was to commit to the program up front so that they could make block purchases of critical components, keep the engineering and mission ops teams together, etc.

To get an idea of what a series of orbital missions at Mars could do, look at the 4 proposed MSO focii: "Report from the 2013 Mars Science Orbiter (MSO) Second Science Analysis Group" http://mepag.jpl.nasa.gov/reports/index.html

[Steve G]

Nasa still needs to eventually land another spacecraft on Mars. Granted, every launch window for Mars has different payload constraints, some are favourable windows, others less favourable, but why not stick the MSL herritage as much as possible? I know the trend is looking towards a sample return mission but the money may simply not be there. If that's the case, keep landing rovers, each with a specific focus and instrumentation, but keep the heritage.