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Mars Sample Return
mcaplinger
post Apr 21 2020, 09:30 PM
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A two-stage solid rocket to be supplied by Northrop-Grumman has been selected for the MAV.

That seems like the right answer to me. The hybrid was a science project and liquids are just too complicated.

https://spaceflightnow.com/2020/04/20/nasa-...es-off-of-mars/

To anticipate a couple of objections John Whitehead will probably have:

1) the TVC for each stage is not shown. Interesting omission.

2) the launch concept is to "eject vertically from the lander in a horizontal position with the first stage motor ignited within a short interval at a predetermined time following the vertical ejection. In order to navigate the MAV safely away from the lander, this could require sudden, high nozzle vector rates on a motor that has been stored at -40C for up to a year." I guess they decided that simply raising the MAV to vertical prior to launch was more complicated than this maneuver. Well, maybe.


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John Whitehead
post Apr 22 2020, 01:37 AM
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Mike, thanks for the link to that long article about MSR and MAV. After carefully reading the article, here are my comments.

Regarding solid rockets being "known," that was said more than 20 years ago, and multiple times since, while the opportunity has been repeatedly missed to build and test prototype MAV stages to get ahead of the schedule crunch. Back then, and now, the fact that a solid rocket motor is not a "stage" tends to be unappreciated by those who say the technology is "known." Key challenges are downplayed, namely the naturally excessive thrust (short burn times) of small solid motors, and the general difficulty of making all the parts lightweight enough. Excessive thrust requires the steering components to be heavier and more responsive than otherwise.

The liquid hydrazine steering on the upper stage is risky, because it might run out. The total propulsive impulse needed there has to be very well understood, because the mass budget cannot tolerate plenty of extra hydrazine. Multiple Earth launch vehicles have failed because they ran out of a fixed supply of hydraulic fluid for steering.

Regarding the 2026 mission schedule, rocket engineering was in the driver's seat for planning the Apollo missions to the moon. The famous Kennedy speech of May 1961 came after JFK asked what could be done, and a rocket engineer (Von Braun) answered in late April of 1961. For MSR, mission planning has forged ahead while MAV engineers stand by the side of the road with their thumbs out, ever hopeful that they will be able to catch up to expectations. At least now it is finally in the budget to begin to do some serious work, but if the 2026 schedule goes by the wayside, will they cut the MAV budget and continue to fund future mission studies, as has always happened in the past?

Seemingly, people don't know that being up against physical limits (such that the components end up too heavy) is a different kind of difficulty from complexity (but hats off to those who are so good at organizing and managing complexity for huge projects). Earlier this year, I reviewed the requirements for the new job opening at NASA HQ, the MSR Program Director. The main criterion was experience leading a major spaceflight program with international collaboration. Considering how that kind of leadership work is typically done, the person hired will probably have the bias that the MAV is a mere subsystem that can simply be bought, like space propulsion typically is. If the person hired has a good understanding of miniature launch vehicles, I may have to eat that hat after tipping it.

Also misunderstood at the tops of org charts is the fact that rocket engineering is a different activity from propellant research. The latter activity is more public and visible, e.g. done in universities, so that's what people think rocket engineering is. Most of the work toward the conceptual hydrid MAV was essentially propellant research. The effort fell short in that domain, never approaching the problem of making flight hardware sufficiently lightweight.

The MAV study done at JPL circa 2015 concluded that the hybrid technology would make the smallest MAV, followed by pump-fed liquid, then pressure-fed liquid, and finally by solid, heavier. Therefore it is interesting to see no further mention of a potential liquid propellant MAV. It is easy to conclude that comparison studies are useless if the technology options do not exist. In this case, the "technology" is not heritage for propellant use in space, but rather it has to be complete working miniature rocket stages that have a sufficiently high ratio of propellant mass to component mass.

I'll continue to look forward to serious MAV progress, however long it takes.
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mcaplinger
post Apr 22 2020, 06:34 AM
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On the two-stage solid MAV design, see https://ntrs.nasa.gov/archive/nasa/casi.ntr...20190030430.pdf and https://ntrs.nasa.gov/archive/nasa/casi.ntr...20190002124.pdf

The first stage burns for 55 seconds with a boost-sustain thrust profile.


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John Whitehead
post Apr 22 2020, 03:43 PM
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Thanks, Mike. Your first link is paper number AIAA 2019-4149, presented in August 2019 at the AIAA Propulsion and Energy Forum. The second link is a paper presented at the (March) 2019 IEEE Aerospace Conference. In summer 2019, I printed them, read them carefully, and wrote many notes in the margins about questions left unanswered.

At first glance, all the graphs, tables, and details shout out, "serious engineering is happening," which presumably impresses decision-makers. Not having time today to look over the details again, here are some of the notes I wrote last year.

AIAA 2019-4149, "A Design for a Two-Stage Solid Mars Ascent Vehicle."
This paper is mostly about solid motor trades, not MAV design, e.g. RCS propellant (liquid steering) not discussed.
No big-picture discussion of why it is hard to build a MAV (making the mass budget close).
No mass budget info, no Isp or deltaV (page 10 has Isp for a long nozzle not used).
Nozzle steering and TVC are left for future work.
Some of the writing was unclear, e.g. at the bottom of page 6 I wrote, "What part of Stage 2 counts as 'second stage mass'?"
On page 7 next to Figure 8 I wrote, "No scale on graph." Their graph says the stage mass fractions are "evolving."
At the bottom of page 9 I wrote, "Complete mass info remains hidden."
A the bottom of page 15 I wrote, "Figure 16 says TVC details are unknown, but the whole thing hinges on whether TVC can be lightweight."
Next to Figure 17, I wrote, "The graph only says their design points have typical shapes, re length versus diameter. So what, already shown in Figure 16. Moot comparison, how about propellant mass fractions?"
The final paragraph says that the mass came out 6 kg below the 400 kg limit, and my note says "error bar uncertainty?"
Overall, I was disappointed enough to mark up the title to, "A Study of Solid Rocket Motor Design Trades for a Notional Two-Stage Mars Ascent Vehicle."

2019 IEEE Aerocon paper, "Mars Ascent Vehicle Propulsion System Solid Motor Technology Plans."
TVC mass is a big open question, but not listed as one of the challenges.
The total mass could be anything (i.e. too heavy), yet it is stated that a design will converge.
Above the intro I wrote, "Can't say the reason for 3 Earth launches, i.e. MAV too big to include on a science mission."
Above Figure 3 I wrote, "No mention of why it is hard to do, or that 40 years of concepts is not much progress."
Above Table 1 I wrote, "Arbitrary rating for rocket motor case materials, where is strength at temperature?"
Above pages 5 and 6 I wrote, "A bunch of math, no physical insight, and not enough info to see big picture or check calculations."
At the bottom of page 5 I wrote, "So how heavy are flex nozzles, and how heavy are TVC actuators and their power supplies?"
Next to Table 4 I wrote, "These differences are minutia compared to the uncertainties between the math and actually building MAV stages."
Above the top of the right column on page 9 I wrote, "TVC actuator mass seems totally unknown."
Overall I was disappointed that the graph axes did not show numbers or units of measure (Fig 4, 5, and others).

Certainly, the engineers are doing the best they can with the limited budget so far, namely more math than hardware. Let's hope that much more progress is being made (or will soon be made) regarding the unanswered questions in the professional publications.

Regarding the boost-sustain thrust profile, this addresses the trajectory concerns I published in 1997 and 2004-2005. it would be nice to see a discussion of how the thrust profile affects propellant mass fraction and-or motor shape (length vs diameter), considering that proven space motors have high propellant fractions, while missile motors with special thrust profiles may not be so good.
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mcaplinger
post Apr 22 2020, 04:32 PM
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QUOTE (John Whitehead @ Apr 22 2020, 07:43 AM) *
Certainly, the engineers are doing the best they can with the limited budget so far, namely more math than hardware. Let's hope that much more progress is being made (or will soon be made)...

If you read the NGIS sole-source procurement (link below) it's for 10 copies of the first and second stage motors and associated TVC. The 10 copies are for 3 demonstration tests, 3 qualification tests, 1 flight test, 1 flight, 1 spare and 1 inert engineering unit.

It doesn't get much realer than that, and there is limited scope for iterative development on the timeline. I can only presume that NGIS (ATK) knows what they're doing; if anyone does, they do.

I share your reservations about the published papers (which are largely high-level parametric "spherical cow" stuff), but in my experience, descriptions of how something will really work rarely get published in advance in the open literature. At least it seems like they are going to cut metal and fly, not just write Powerpoints, and that's always a good sign.

https://beta.sam.gov/opp/349cbd728ab24d7693...true&page=1


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stevesliva
post Apr 22 2020, 04:47 PM
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QUOTE (mcaplinger @ Apr 22 2020, 12:32 PM) *
I can only presume that NGIS (ATK) knows what they're doing; if anyone does, they do.


Granted I can't keep track of all the consolidation, but given the number of SLBMs, SAMs, AAMs, etc that use solid rocket motors, there's probably a few others in the defense industry.
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mcaplinger
post Apr 22 2020, 05:47 PM
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QUOTE (stevesliva @ Apr 22 2020, 08:47 AM) *
Granted I can't keep track of all the consolidation, but given the number of SLBMs, SAMs, AAMs, etc that use solid rocket motors, there's probably a few others in the defense industry.

Within the US, only Aerojet Rocketdyne AFAIK. And I didn't say there wasn't anyone else, only that ATK clearly has a lot of experience and NASA decided was the only suitable manufacturer (hence the sole source contract.)


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Brian Swift
post Apr 25 2020, 07:42 AM
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They also have a nice rocket garden worth checking out if one happens to be near Promontory UT.DSC08644 by bswift, on Flickr
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John Whitehead
post May 6 2020, 05:48 PM
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QUOTE (mcaplinger @ Apr 22 2020, 05:32 PM) *
If you read the NGIS sole-source procurement (link below) it's for 10 copies of the first and second stage motors and associated TVC...
It doesn't get much realer than that...

Yes, I read this news in early April, a welcome step toward "real work" on a MAV. Here is the question that I think no one can answer for sure. Will it turn out to be a "design and build" engineering effort, or a "trial-and-error" research and development effort? Both count as "real work" in my book. If it turns out to be "only R&D," the effort needs to continue until there is a mission-capable MAV, regardless of the overall schedule for MSR.

Regarding the nice image from Utah posted by Brian Swift, my understanding is that the small rocket motors are made in Elkton, Maryland. At least that is where Thiokol historically made the STAR series of solid rocket motors for space applications.
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Quetzalcoatl
post Nov 11 2020, 04:17 PM
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Bonjour ŗ tous,

Delayed launch again !?! sad.gif

https://www.nasa.gov/sites/default/files/at...eport_small.pdf
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Explorer1
post Nov 12 2020, 02:57 AM
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Some good details about the MAV's future development in this report (pages 5, 6 and 7 in the summary).
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Quetzalcoatl
post Nov 12 2020, 12:29 PM
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yes, thatís a positive aspect. rolleyes.gif
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mcaplinger
post Nov 13 2020, 07:32 PM
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QUOTE (Explorer1 @ Nov 11 2020, 06:57 PM) *
Some good details about the MAV's future development in this report (pages 5, 6 and 7 in the summary).

Frankly, I find the concern about thermal cycling of the MAV solid motors, and the suggestion to add an RTG to the lander to heat the MAV to reduce thermal cycling, to be a massive step backward from the seeming progress of letting the contract to buy the SRMs discussed upthread.

This is the kind of "adding epicycles" that signals that a program is in trouble IMHO.


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