Mars Sample Return Options

[John Whitehead]

Thanks for that article Mike, it is great to see test progress for the MAV SRMs. Ideally the news writers would distinguish Earth departure from Mars departure, both referred to as "launch" in the article: "first launch of a rocket from the surface of another planet" and "MAV is currently set to launch in June 2028" (latter from Earth).

Good to see that the first stage motor test included Mars-like environmental conditions (low temperature, low density atmosphere). The second stage test apparently showed that the propellant can burn and make thrust while the motor is spinning. The test constrained the spin axis with a bearing, so there is more to be done to be sure that Stage 2 will not wobble too much in flight. We can also wonder how heavy the test articles were, and how much effort with more testing will be needed to trim down to flight weight.

It is interesting to compare the MAV to Ingenuity, which was described as a technology demo on Mars 2020, then celebrated as a surprising triumph when it worked. The helicopter engineers were not surprised, because four versions had been built and thoroughly tested under Mars-like conditions to refine the design, according to Aerospace America in January 2023 <https://aerospaceamerica.aiaa.org/departments/martian-aviator/> In contrast, the MAV is mission-critical for the most expensive planetary program ever, and it might not be fully flight tested.

[djellison]

because four versions had been built and thoroughly tested under Mars-like conditions

None of the engineering models flown in the 25ft space simulator could be considered flight-like in terms of flying. Martian vs Terrestrial gravity precludes it.

The MSL / M20 Descent Stage / Skycrane was never "fully flight tested" either.

[Explorer1]

They had a a tether to decrease the weight to simulate as best they could, right? Or do you mean something different?
https://www.jpl.nasa.gov/news/nasas-mars-he...es-flight-tests

The team accomplished this with a gravity offload system - a motorized lanyard attached to the top of the helicopter to provide an uninterrupted tug equivalent to two-thirds of Earth's gravity. While the team was understandably concerned with how the helicopter would fare on its first flight, they were equally concerned with how the gravity offload system would perform.

Similar to the photos/videos released of the MAV 'toss' tests from last year.

[StargazeInWonder]

The moments when the MAV is airborne (or whatever the correct term might be, regardless of "air") would be the same on Earth and Mars, no? Free fall is free fall.

[Explorer1]

True, but there will be more of those moments on Mars than for equal mass on Earth! More leeway of time to ignite the solids is very welcome (and it will be quite a sight...)

[djellison]

would be the same on Earth and Mars....

Different temps, different atmospheric density.

Best test environment for it is a high altitude balloon drop test (see things like LDSD, viking parachute tests) but even then you're not launching it from the surface using the VECTOR mechanism, the atmospheric profile isn't what you would get at Mars, the IMU is going to be getting very different info etc etc etc.

You can't test something like the MAV end to end on Earth. You can test lots of piece of the puzzle (some larger than others) and then you bridge the various tests together as an assemblage of tests in simulation.

Same as for Skycrane.

Same as for the Chopper which had gravity offload tests in the the 25ft space simulator ( https://www.youtube.com/watch?v=tMCJGfwj3rY ) but it wasn't taking off from the surface, wasn't turning or flying, it was using outside in tracking and cables in to the chopper to tell it what to do....then there were much lighter engineering models that didn't have to be gravity offloaded but had external power cables etc etc.

Test what you can. Model what you can't. None of it is perfectly flight like.

[mcaplinger]

Test what you can. Model what you can't.

Yep. Considering that some reports suggest that MSR has severe cost difficulties already, expecting some full-up flight test which would have limited fidelity anyway is simply not in the cards.

Presumably the MAV subs (NGC and Lockheed Martin) have access to many decades of experience on solid rocket propulsion and control from military programs.

[John Whitehead]

History shows it is not easy to model whether a new launch vehicle is going to work the first time, so here is a worthy version of "Test what you can. Model what you can't."

Test what you can
From a balloon or a sounding rocket, launch the MAV at high altitude over Earth, at atmospheric densities and temperatures similar to Mars, like testing EDL parachutes. Plan a trajectory (hundreds of miles suborbital) with maneuvers that challenge the navigation and steering systems a little more than the real mission, and measure margins such as remaining steering propellant on Stage 1 after Stage 2 separates. The solid rocket motor thrust is sufficiently high that flight speeds in testing will not be hugely affected by the extra gravity over Earth (thrust to mass is roughly 2 to 4 Earth g's from start to end of the Stage 1 burn). When testing above Earth, you have the luxury of high-bandwidth telemetry with the MAV reporting its own position versus time. Use GPS as a diagnostic only, with the MAV guidance relying on what it will have for Mars (IMU). Analyze the data to see how much the path deviated from the planned trajectory over Earth.

Model what you can't test
Use the results from the flight over Earth to plug into your flight model for Mars, to determine the trajectory that would be expected starting on Mars.

Repeat the above steps until there is a MAV that can reach the desired Mars orbit.

Most flight control expertise from military programs is not directly applicable to the MAV, because small missiles use fins for steering in Earth's relatively thick atmosphere. The raw performance needed for the MAV exceeds the capability of military missiles of its size, as discussed previously in this forum. A raw performance challenge (Mars helicopters and MAV) is a different animal compared to something that is primarily a complexity challenge (EDL).

Professional publications and NASA planning documents have referred to the importance of flight testing the MAV, including Lockheed warning NASA about the risk of not testing (see Post #456 in this forum).

[john_s]

Independent Review Board assessment of MSR was just released. Key findings (not good):

- "...there is currently no credible, congruent technical, nor properly margined schedule, cost, and technical baseline that can be accomplished with the likely available funding".

- "Technical issues, risks, and performance-to-date indicate a near zero probability of Earth Return Orbiter / Capture Containment and Return System or Sample Return Lander / Mars Ascent Vehicle meeting the 2027/2028 Launch Readiness Dates (LRDs). Potential LRDs exist in 2030, given adequate funding and timely resolution of issues.

- "A 2030 Launch Readiness Date for both Sample Retrieval Lander and Earth Return Orbiter is estimated to require ~$8.0-9.6B, with funding in excess of $1B per year to be required for three or more years starting in 2025"

Space News writeup here.

John

[BYEMAN]

The second stage test apparently showed that the propellant can burn and make thrust while the motor is spinning.

A test wasn't required to determine that. Spinning solid motors have been used 100's of times

[John Whitehead]

A test wasn't required to determine that. Spinning solid motors have been used 100's of times

Sorry if my sarcasm was too subtle. Does anyone know the purpose of burning the second stage propellant grain while spinning on a bearing? Could they have been measuring off-axis forces and torques? I worry that the purpose was to fool someone(s) whose understanding goes "word deep" and needed to hear that a "spin test" was done.

A far more informative spin test would fire the little circumferential motors for spin-up and then for de-spin, with the MAV upper stage in free fall (drop tower e.g.). Repeat that with different imperfections in the spin motors (misalignments and unequal impulses). Also different stage mass properties to represent the range of imbalances after the sample tubes are installed on Mars. The results would indicate the margins available for being able to obtain Stage 2 thrust in the desired direction without too much wobble. With or without using a drop tower initially, such testing should be done at high altitude so there is time to fire the main motor in between spin-up and de-spin, and see if it flies straight enough.

[Steve G]

A not unexpected review for MSR.

https://spacenews.com/nasa-starts-reassessm...n-architecture/

[John Whitehead]

The article linked in Post #492 refers to the October 20 MEPAG meeting. In response to one question in that meeting, the Chair of the 2023 MSR Independent Review Board (IRB) said that none of the members had expertise for small scale launch vehicles, but they did have access to the MAV team and the MAV PDR reviewers. Looking over the IRB report (first link in Post #489) leaves the overall impression that the new cost estimate is primarily related to the big picture of managing the complexities of implementation, with relatively less consideration of particular technology challenges. Attached below are a few pages from the IRB report with notes added (MSR IRB 2023Sep1 Notes.pdf).

In the MEPAG meeting the MSR Chief Engineer was introduced (apparently a new job slot at NASA HQ). The additional technical oversight should be beneficial to mission success.

Attached File(s)

 MSR_IRB_2023Sep1_Notes.pdf ( 548.54K ) Number of downloads: 52

 

[Explorer1]

A Planetary Society interview with the head of the independent review board. Some very interesting details. Starts around 26 minutes (transcript available too):
https://www.planetary.org/planetary-radio/s...-wrong-with-msr

[mcaplinger]

A Planetary Society interview with the head of the independent review board. Some very interesting details.

Hmm. I'll admit that reading transcripts is always very difficult, but nothing leapt out at me that I would have called an interesting detail. What specifically are you reacting to?