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Mars Sample Return
mcaplinger
post Aug 14 2018, 12:17 AM
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QUOTE (JRehling @ Aug 13 2018, 02:22 PM) *
This discussion in 2018 certainly highlights how wildly optimistic that was

If we had tried to do it, we'd have figured out how. It's these endless paper studies that go nowhere.


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stevesliva
post Aug 14 2018, 03:13 PM
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QUOTE (John Whitehead @ Aug 9 2018, 02:06 PM) *
Yes, there needs to be rocket engineering, not rocket science. But MAV funding is being spent on "rocket science" (propellant research), instead of engineering to improve the state of the art. There needs to be an engineering effort to make propulsion components less than half as heavy as typically used for satellites and spacecraft. Whether or not this counts as "new technology" is only semantics.


The first part is semantics, too.

Your point, to me, is that declaring the technology ready to snap into a typical "we're sending a spacecraft to mars" schedule is aiming to take 9 women and make a baby in a month.

It's a bit of a catch-22 where you can't get the money and staffing to solve the problem until you say with certainty that the problem is fully solvable with whatever time and money budgets allow. Things then slip right later but the project survives.
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John Whitehead
post Aug 18 2018, 09:20 PM
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QUOTE (Gerald @ Aug 13 2018, 10:52 AM) *
...composite tanks for cryogens (of 2005)...
...3D-printed_space_part... apply these findings to MSR...

Regarding composite tanks, there are at least three distinct applications for space flight.
1. High pressure gas storage, typically helium on spacecraft, satellites, and launch vehicles. Composite overwrapped pressure vessels (COPVs) have been widely used since about 1990. Before that, thick-walled titanium vessels were the standard. COPVs work well, because the thick walls needed for high pressure requires many layers of fiber wrapped over a metal liner. Having many layers makes the design tolerant to a flawed fiber or a misplaced fiber.

2. Composite tanks for liquid propellants on satellites and spacecraft. Typically the pressures are so low and tanks are so small, that the state of the art is still all-metal titanium walls, about a millimeter thick or less. Research projects at JPL and elsewhere have made serious efforts, but there needs to be just a few layers of fibers wrapped onto unusually thin metal, in order to be lighter overall than plain titanium tanks. Despite decades of hopes for lighter composite liquid tanks, they are essentially all still just titanium on satellites and spacecraft.

3. Composite tanks for cryogenic propellants on launch vehicles. Gerald, thanks for that link to the 2005 article, which documented the challenges and partial successes at that time. More recently, some good news is that Rocket Lab has apparently succeeded at using composite material for the liquid oxygen tanks on the Electron launch vehicle. Compared to a tiny MAV, the Electron's relatively large diameter tanks have thick enough walls so that there are many layers of fibers.

Regarding 3D printing, I agree that offers a lot of possibilities for making lighter weight MAV components. This applies to pieces that previously had extra unnecessary metal as a result of geometrical complexity (brackets, valve bodies, etc.). However, major components such as propellant tanks don't have extra metal that can be left out. Just last month, Lockheed Martin announced 3D printing of a titanium satellite tank, to save time and money, but not for less mass.
https://news.lockheedmartin.com/2018-07-11-...ted-Space-Parts
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John Whitehead
post Aug 18 2018, 10:40 PM
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QUOTE (mcaplinger @ Aug 14 2018, 12:17 AM) *
It's these endless paper studies that go nowhere.

Agreed. This group discussion got me curious about the earlier history of MSR. Back in the 1980s, the big mission study was MRSR (Mars Rover Sample Return, when rovers were still in the future). This past week I looked up some of the professional publications (AIAA) from 1988 and 1989. In at least one scenario, the MAV was going to be about 1.5 metric tons, with a pump-fed engine so that the propellant tanks could be low-pressure and therefore lightweight. The particular pump-fed engine in the study, the XLR-132 (an Air Force project, XLR = experimental liquid rocket), had development difficulties and was never fully brought to fruition. If researchers would publish technical papers on exactly why it is difficult to make smaller pump-fed engines, that would make a huge contribution to MAV decision making, but generally negative results are less likely to be published.

A more interesting piece of history turned up when I searched the Internet for "Mars Rover Sample Return." The following link is a 2011 interview with Brian Wilcox, a rover engineer who started at JPL in 1982. Scrolling about halfway through the interview, there is a major heading for MRSR.
https://ethw.org/Oral-History:Brian_Wilcox
While the entire interview is fascinating, one striking thing he says is that at one time, there was a debate about whether rovers were needed. Mars scientists were concerned that Mars-bound payload mass used for rovers would reduce the number of scientific instruments that could be sent. This science perspective seems consistent with hoping for a MAV that is super-tiny and doesn't cost anything (i.e. doesn't require building a new team of specialists).

Thinking back, I recall being in one MAV meeting at JPL, around 2006, when one of my propulsion friends introduced Brian as "our GPG," which was then explained as "general purpose genius," quite a compliment. Also the interview reminded me of being invited to a "Mars Mobility Workshop" at NASA Ames in 1995. As an engineer since the 1980's and a space enthusiast since before Apollo, I always figured that Mars rovers were going to happen, so I probably did not fully appreciate the purpose of that meeting in 1995. Brian's interview recalls "a guy named Mike Carr" working to turn the tide in favor of rovers, and I do recall Mike Carr leading the discussion, while other geologists in the room had little to say. I found my old file folder and sure enough, Brian and other Mars heavy-hitters were at that meeting. Attached to this post as an upload to UMSF, I made a composite PDF to show the attendee list along with my name tag, at the bottom of Mike Carr's letter that was distributed after the meeting (hope the PDF comes through OK).
Attached File(s)
Attached File  MarsRoverMobilityAmes1995.pdf ( 67.12K ) Number of downloads: 71
 
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mcaplinger
post Aug 19 2018, 06:49 PM
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QUOTE (John Whitehead @ Aug 18 2018, 02:40 PM) *
Thinking back, I recall being in one MAV meeting at JPL, around 2006, when one of my propulsion friends introduced Brian as "our GPG," which was then explained as "general purpose genius," quite a compliment.

Wilcox was the main proponent of the all-solid mini-MAV based on his father's work on NOTSNIK. https://www.airspacemag.com/space/the-one-p...-718812/?page=1

and per
https://www-robotics.jpl.nasa.gov/people/Br.../personFull.cfm
QUOTE
Awarded the JPL Award for Excellence, JPL's highest award, in May 1999 for proposing the Miniature Mars Ascent Vehicle. In the words of JPL Director Ed Stone at the award ceremony, this effort "enabled Mars sample return."


But of course in engineering the devil is in the details, and either the mini-MAV was not as workable as originally thought, or the concept just wasn't followed through to the end.


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JRehling
post Aug 19 2018, 08:43 PM
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QUOTE (John Whitehead @ Aug 18 2018, 03:40 PM) *
one striking thing he says is that at one time, there was a debate about whether rovers were needed.


This is something that couldn't be settled without knowing how diverse potential (and feasible) landing sites are. If a landing site is homogeneous then there is truly no need for mobility. That's one reason why the Phoenix lander worked well without mobility.

Opportunity (a bit by luck) and Curiosity (by design) have demonstrated exceptional heterogeneity of landing sites. Spirit (a bit by bad luck) somewhat less so. If Spirit had not exceeded its planned longevity, it might not have returned much value in return for its mobility. Opportunity did so the first day it drove.
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John Whitehead
post Aug 19 2018, 08:52 PM
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QUOTE (mcaplinger @ Aug 19 2018, 06:49 PM) *
...father's work on NOTSNIK...
...mini-MAV was not as workable as originally thought...

Early in 2018, a team in Japan set a record for the smallest launch vehicle (about 3 metric tons) to ever deliver a satellite to Earth orbit (a cubesat that remained spinning).
https://www.nasaspaceflight.com/2018/02/jap...orbital-launch/
This NSF article describes the 3-stage solid, which had similarities to the Mini-MAV concept, so it is good to see the principle proven. The article also mentions the NOTSNIK attempts of 1958, aka "the US Navy’s NOTS-EV-1, or Pilot."

Yes Mike, Brian's Mini-MAV evolved into a much heavier two-stage solid, after years of studies by the best available technical experts (see Post #324, second paragraph). But of course building and testing, much more expensive, is needed to actually advance the state of the art. For concepts that are deemed unworkable, it would be nice to see published technical explanations for "why not." My own recollection and understanding is that the Mini-MAV had little or no telemetry, little or no active navigation, and the tiny payload would remain spinning in Mars orbit. All these features were judged to be too risky. Also the requirement for payload mass increased. Even over the past few years, the MAV payload mass has remained unsettled, so even if MAV technology could be in the bag today, there would still be no firm decision for how big to build an actual MAV.

A couple more thoughts. At the time that the Mini-MAV was celebrated (circa 1999), my impression was that no one had done detailed trajectory calculations, in particular the fact that aerodynamic drag becomes more important for smaller rockets, even in the thin atmosphere of Mars. Also an unguided Mini-MAV would need a heavier support structure on the ground to initially point it in the correct direction. Japan's SS-520 rocket noted above illustrates both of these principles, because it was unusually skinny for its length (to avoid undue drag), and it initially slides along a rigid launch rail on the ground.
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mcaplinger
post Aug 20 2018, 12:05 AM
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QUOTE (John Whitehead @ Aug 19 2018, 12:52 PM) *
For concepts that are deemed unworkable, it would be nice to see published technical explanations for "why not." ... Also the requirement for payload mass increased.

As you pointed out, there's no real motivation to publish engineering approaches that don't pan out; at best this usually remains a part of the design lore within a given organization, and at worst it's forgotten by the next generation even within the same organization.

In hindsight to my inexpert eye, the Mini-MAV was an example of something that sounded workable as a high concept and turned out to be less attractive on closer examination; there has also been a lot of risk aversion for things like grain cracking that could be easily avoided with a little thermal control and limiting time on the surface.

As for the payload mass, the science community does themselves no favors by constantly racheting up the minimal requirement for worthwhile sample return. At one point a small grab sample from a single known point was considered a useful minimum; now it seems we have to have a separate rover to carefully pick samples and curate them. Maybe that's a legitimate evolution of scientific thinking, but it's obviously not helping reduce costs. As usual, these missions are always approached as being the single chance to do something, so they become all things to all people instead of having a focused, minimalist goal.


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John Whitehead
post Sep 10 2018, 03:38 AM
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QUOTE (mcaplinger @ Aug 20 2018, 12:05 AM) *
the science community does themselves no favors by constantly racheting up the minimal requirement for worthwhile sample return. At one point a small grab sample ...

Michael, I agree with your concern, although the amazing science progress in recent years has probably overshadowed the value of a scoop of soil. At least my understanding is that rock core samples will be much more valuable. As far as how many rock samples, yes that would directly affect MAV size.

One piece of recent news that we all missed in last month's discussion, is that the National Academy released a draft of their mid-term report on the planetary science decadal survey.
http://www8.nationalacademies.org/onpinews...?RecordID=25186
Links in the article lead to the National Academy Press web pages, where I was able to download the report by declaring "guest" status. The intent is that this is an independent five-year evaluation of how NASA is doing on their current ten-year plan. Among other things, the Mars chapter says that reasonable progress is being made toward a MAV, and shows images like those in the 2018Feb20 presentation from JPL to MEPAG. This is notable, considering that the previous mid-term report ten years ago gave NASA a failing grade for lack of MAV progress. Presumably there was a strong incentive to have a record of progress this time around.

My assessment is that the National Academy committee did not ask critical questions, just like at the MEPAG meeting in February. Uploaded with my post here is a PDF document, 5 pages from the JPL presentation to MEPAG with my comments, mostly in the form of questions that could be asked.
HybridMAVcomments2018Sep2jw.pdf

Lastly, I dug a bit more into the "ancient history" of MSR. A 1988 presentation by the Director of the NASA Johnson Space Center is titled, "Mars Rover Sample Return Mission Delivery and Return Challenges." The printed paper (AIAA 88-5007) devotes 4 pages to sending the required items to Mars ("delivery"), and only one page to the return challenges. The latter page says that the MAV will launch, then lists the challenges as sample preservation, rendezvous and docking in Mars orbit, planetary protection, and several steps that have to happen upon reaching Earth. I remain astonished that the MAV is mentioned but not noted as a challenge. Apparently there was a long tradition of assuming that it would be straightforward to design and build a MAV.
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Attached File  HybridMAVcomments2018Sep2jw.pdf ( 384.2K ) Number of downloads: 63
 
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mcaplinger
post Sep 11 2018, 08:42 PM
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QUOTE (John Whitehead @ Sep 9 2018, 07:38 PM) *
My assessment is that the National Academy committee did not ask critical questions, just like at the MEPAG meeting in February. Uploaded... my comments, mostly in the form of questions that could be asked.

Seems to me that neither the NAS folks nor MEPAG ask good technical/engineering questions very often. IMHO, they seem surprisingly credulous of the engineers who are basically trying to sell them something.

As to your comments: this is essentially a series of cartoons, not a technical document. I think your questions are well-founded in most cases. The operating temperature of -20C is not unreasonable (-100C would have been, maybe -20C was a typo) and probably not terribly driving if the AFTs on page 3 are to be believed. I share your skepticism about whether the case has been made for the hybrid.


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Explorer1
post Sep 11 2018, 09:48 PM
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How would one go about testing a prototype (or flight) MAV, especially in the proper atmospheric pressure? Could you test in a chamber that gradually lowered the pressure from surface to vacuum to simulate ascent, or would some sort of high altitude balloon/ sounding rocket launch work instead, as was done for the LDSD a few years back?
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mcaplinger
post Sep 12 2018, 02:56 PM
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QUOTE (Explorer1 @ Sep 11 2018, 01:48 PM) *
How would one go about testing a prototype (or flight) MAV, especially in the proper atmospheric pressure?

Small rocket motors can be tested in vacuum chambers. https://www.nasa.gov/image-feature/firing-u...et-engine-tests Larger ones for which this would be impractical are usually tested with a modified nozzle or some kind of diffuser to try to simulate the effects of lower pressure under ambient conditions.

I don't know of any test that tries to simulate the ascent pressure profile, but I don't think that's critically important going from 6 mbar to vacuum.

You can learn a lot from a sea-level static test, especially for a simple solid or hybrid motor like those being considered. Whether that's sufficient testing, especially in a very risk-adverse situation, is debatable.

I'm not saying it was equivalent, but it's not like a system like the MSL sky crane was ever tested in flight before it got to Mars.


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Tom Dahl
post Sep 12 2018, 10:43 PM
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QUOTE (Explorer1 @ Sep 11 2018, 05:48 PM) *
...or would some sort of high altitude balloon/ sounding rocket launch work instead, as was done for the LDSD a few years back?

FYI, in the early 1970s a similar technique was used to validate the supersonic Disc-Gap-Band (DGB) parachute or decelerator designed for the Viking '75 project, along with its mortar-sabot ejector mechanism. There was a series of Balloon Launched Decelerator Test (BLDT) flights. For the supersonic test flights the flight article was accelerated via four rocket engines built into the aeroshell capsule.

The same basic DGB parachute design has been used on all landed Mars missions since Viking, as I recall - along with Viking's 70-degree sphere-cone aeroshell shape.
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John Whitehead
post Sep 14 2018, 02:54 PM
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Engineering publications from JPL show that as of mid-2017, there was a plan to build a low-performing (heavy components) version of the hybrid MAV for a test launch starting at a high altitude above Earth (AIAA 2017-4900) but as of mid-2018, the priority shifted to hurry up and build a real MAV sooner, with a less certain plan for terrestrial flight testing (AIAA 2018-4834).

A greater concern than atmospheric pressure is whether the wax-based fuel will have a melted layer or a soft layer behind the flame front, which would tend to flow or slump toward the aft end of the rocket while accelerating at multiple Earth g's. That would be a show-stopper for this particular propellant, or at a minimum, the fuel grain would have to be tailored specifically for the acceleration profile, with extra fuel toward the top end.

In any case, something completely new like a MAV absolutely needs flight testing. Any MAV will be a completely different beast from Mars descent propulsion, which is based on proven propulsion technology used widely on satellites and spacecraft, all of which are similarly built and flown without testing whole propulsion systems.
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mcaplinger
post Oct 28 2018, 12:33 AM
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QUOTE (mcaplinger @ Aug 19 2018, 04:05 PM) *
As for the payload mass, the science community does themselves no favors by constantly racheting up the minimal requirement for worthwhile sample return.

Case in point:

https://www.theguardian.com/science/2018/oc...s-sample-return
QUOTE
“The community prefers a mega-mission,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena. “If we’re going to do sample return, it has to be a sample cache for the ages.”



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