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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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Disclaimer: This post is based on public information only. Any opinions are my own.
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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 Yesterday, 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 Yesterday, 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: 7
 
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