Mars Sample Return Options

[StargazeInWonder]

The Soviet Luna ascent stages had a mass of 520 kg (that was for Earth-intercept, which requires somewhat more energy than merely lunar orbit). The lightest rocket to reach Earth orbit has a mass of 2620 kg. So presumably the MAV will have to have a mass in the lower end of that range.

[John Whitehead]

Committing to the Mars Ascent Vehicle represents an early and concrete step to hammer out the details...said Thomas Zurbuchen, the associate administrator for science at NASA Headquarters.

Hmmm, re "early" and "details."

If I had written that news release, he would have been quoted as saying, "...long-awaited, long-postponed, widely underestimated step to create a miniature launch vehicle beyond the known state of the art."

In Space News this week, Jeff Faust noted that we still don't know if the MAV can be small enough to fit on the same lander with the fetch rover.
https://spacenews.com/lockheed-martin-wins-...-sample-return/

[John Whitehead]

Angie Jackman...is the Mars Ascent Vehicle project manager..."We are working to transform the Mars Ascent Vehicle from a drawing-board concept to an executable project,” Jackman said. “We went through exhaustive design iterations to reduce vehicle mass..."

Nice article about the MAV team and its manager. She has been associated with MAV efforts for at least three years (her name is in the acknowledgments for AIAA 2019-4149, A Design for a Two-Stage Solid Mars Ascent Vehicle, by Prince et al).

The above AIAA paper says that the concept for the unguided spinning upper stage was considered but then abandoned because total propulsive capability would need to be higher to compensate for less orbit accuracy. But as of 2021, the unguided spinning upper stage was selected as the best option to make the MAV small enough to send to Mars.

As usual, my own expectation is that reducing vehicle mass will need building and testing well beyond what the above quoted news article says, "exhaustive design iterations" as a "drawing-board concept."

Attached File(s)

 SpinningUpperStageMAV2019.pdf ( 169.66K ) Number of downloads: 180

 

[bobik]

Integrated Design Results for the MSR DAC-0.0 Mars Ascent Vehicle. [Paper][Presentation]

Integrated Design Results for the MSR SRC Mars Ascent Vehicle [Paper][Presentation]

SRC [Systems Requirements Cycle] performed November 2020 - June 2021. This was MAV’s second major development cycle. -> The primary purpose of SRC was to develop the system-level requirements for the vehicle in preparation for the System Requirements Review (SRR), held November 2021. SRR passed successfully. -> Following SRR ... campaign architecture shift to dual landers. -> increased mass allocation for MAV [-> larger SRMs with larger mass margins] at expense of budget [-> reduced scope of flight test]

[John Whitehead]

Thanks bobik for posting links to the latest MAV design info from the recent 2022 IEEE Aerospace Conference (UMSF is lucky in this case that Government work is not subject to copyright). Lots of nice CAD images and detailed analyses. The MAV mission is described as "Risk Class A," which means that a high priority will be placed on doing everything possible to be sure it will work.

Regarding the unguided spinning upper stage, the paper says that the "trajectory and orbital performance is extremely sensitive to tip-off rates and vehicle pointing error during staging." The authors wrote that the Mars samples will result in an "unknown payload mass distribution." I did not see a specific mention of the significance (of sample masses) for correct pointing and spinup.

Besides the upper stage risk, the biggest overall unknown is presumably the total MAV mass. The MAV "target mass allocation" is stated to be 400 kg.

[Explorer1]

Regarding the unguided spinning upper stage, the paper says that the "trajectory and orbital performance is extremely sensitive to tip-off rates and vehicle pointing error during staging." The authors wrote that the Mars samples will result in an "unknown payload mass distribution." I did not see a specific mention of the significance (of sample masses) for correct pointing and spinup.

Can't they estimate the masses of each sample from Perseverance? The atmosphere samples will obviously be lighter than the rock samples, and the coring process tells us the density (and thus mass) of the solid samples? The fetch rover can then arrange them in the most optimal manner when loading them onto the MAV to keep everything as balanced as possible.
All issues with doing payload integration on another planet...

[StargazeInWonder]

This is a big change to the plans:

"NASA Science Mission Directorate head Thomas Zurbuchen reported on Monday that the agency is reworking the architecture of its flagship Mars Sample Return (MSR) mission… Previously, the plan was to use a single lander to convey both an ESA-built rover that will retrieve cached surface samples and an ascent vehicle that will bring the samples into space. Now, two landers will be used."

"The samples will be delivered to the ascent vehicle by the ESA rover and ultimately transferred to an ESA-built orbiter, which will transport them to Earth. […] both landers launching in 2028, the retrieved samples are expected to arrive back at Earth in 2033. As before, ESA’s orbiter is slated to launch in 2027."

https://www.aip.org/fyi/2022/plans-scramble...p-mars-missions

[vjkane]

This is a big change to the plans:

"NASA Science Mission Directorate head Thomas Zurbuchen reported on Monday that the agency is reworking the architecture of its flagship Mars Sample Return (MSR) mission… Previously, the plan was to use a single lander to convey both an ESA-built rover that will retrieve cached surface samples and an ascent vehicle that will bring the samples into space. Now, two landers will be used."

"The samples will be delivered to the ascent vehicle by the ESA rover and ultimately transferred to an ESA-built orbiter, which will transport them to Earth. […] both landers launching in 2028, the retrieved samples are expected to arrive back at Earth in 2033. As before, ESA’s orbiter is slated to launch in 2027."

https://www.aip.org/fyi/2022/plans-scramble...p-mars-missions

Here is a link to Dr. Z's slides. Sample return plans start on slide 24, but slide 23 is Clipper update, and slide 24 is Roman update, which are likely to be of interest, too.

Using a separate lander for the fetch rover has been discussed as an option for some time now that I'm aware of. A couple of years?

[mcaplinger]

Using a separate lander for the fetch rover has been discussed as an option for some time now that I'm aware of. A couple of years?

The April 2020 mission overview https://mepag.jpl.nasa.gov/meeting/2020-04/...erview%20V3.pdf clearly shows just one launch for the MAV and fetch rover. They've been holding the option open to split this in case of mass growth for a while, but it doesn't speak well to the maturity of the design IMHO.

Jan 2021 also shows one launch for fetch rover and MAV. https://mepag.jpl.nasa.gov/meeting/2021-01/...1_2021%20V5.pdf

[John Whitehead]

The March 23 American Institute of Physics (AIP) article (link in Post #427) reminds us that the two-lander option was already being considered in mid-2020, made public in the IRB report in November 2020 (link in Post #385, see also a summary of 2020 events in Post #389).

As of mid-2021, the MAV team at MSFC was already planning for two landers (Mars Lander Vehicle in addition to the Sample Return Lander), and they expected that 2028 would be the earliest departure from Earth (see points 1 and 2 in Post #407).

MSFC also told the MAV bidders that the MAV would be 450 kg (see Point 1 in Post #407), in contrast to the 400-kg "target mass allocation" from the recent IEEE Aerospace Conference (Posts #424-425).

Presumably the recent "big change to the plans" (Post #427) resulted from a delayed realization at HQ that 400 kg is not within reach.

The AIP article says nothing about the MAV design, so we might hope that a separate lander can make it possible to put guidance back on the upper stage instead of taking a big risk with the spinning upper stage, done only for mass reduction (an idea that was declared "abandoned" by MSFC in 2019, see the attachment to Post #423).

A smaller MAV might have been possible, if the past 45 years of hopes for MSR had included a dedicated program to create, design, build, and test new technology for miniature launch vehicles (not to be confused with propellant research). For a detailed explanation of the overall MAV situation, see the October paragraph in Post #389 for the three MEPAG links on the JPL website.

[StargazeInWonder]

There's really nothing in the history of unmanned spaceflight with such a complex architecture as this four-flight mission, or even close to it. On the other hand, this change represents a move towards reducing ambition/complexity, or at least reducing the complexity per launch… It still means that success would depend upon three successful launches from Earth, two successful landings on Mars, one successful Mars orbit injection, one successful launch from Mars, successful ground operations on Mars, successful rendezvous and transfer in Mars orbit, and one successful return to Earth. Ten successes in a row is a high standard to hit.

[Explorer1]

Some details in this article with choice quotes:
https://spacenews.com/nasa-to-delay-mars-sa...ander-approach/

The single-lander approach would require a larger heat shield, estimated to be 5.4 meters in diameter, which in turn would require a larger payload fairing for the rocket launching it. The design also had “unproven” entry, descent and landing capabilities and would require electric propulsion on the cruise stage to increase its payload performance.

A dual-lander approach, he said, could make use of the same landing system used by Perseverance and, before that, Curiosity. “It can be completed in the ’20s, just like we want to,” he said, and avoids the complexity of the larger design.

Both NASA and ESA agreed to adopt the approach as well as a schedule that would delay the launches of the two landers to 2028. The Earth Return Orbiter would launch in 2027, and the samples would return to Earth in 2033 under that revised schedule.

2033 is still the notional return date, I see. I think it's a good tradeoff, minimizing the time spent on Mars.

MAV + arm to be built by JPL, but decision on fetch rover + lander to be made by June.

[John Whitehead]

Here are comments from reading the recent MAV design publication (see Post #424-425).

Mass budget insights from trajectory simulation
MSFC published propellant masses and burn times for both stages, perhaps because these need to be finalized for the solid rocket motor contract, while other mass numbers remain uncertain. For a 16-kg payload to a 380-km orbit, the MAV mass goal is 400 kg. Using the published numbers, I ran gravity turn trajectory simulations for 400, 425, and 450 kg. The attached table of simulation results (see below) shows trends for the fixed propellant masses and burn times. As the MAV gets heavier, Stage 1 delta V decreases while its trajectory becomes steeper, and total delta V increases so that significantly more delta V is needed from Stage 2.

It may not be easy to make all the Stage 1 parts lightweight enough for a 400-kg MAV, while the 450-kg MAV shifts the same challenge to Stage 2 (see stage propellant fractions near bottom of table). The MSFC paper refers to a delta V margin, with a more complicated trajectory to expend the excess. Indeed, starting from any workable design point, a Stage 2 improvement (higher propellant fraction) will yield extra delta V while permitting Stage 1 hardware to be heavier for the same total MAV mass.

Spinning the upper stage (to avoid carrying guidance and control components) is seen as the key to improving Stage 2 delta V. A remaining big mass contributor to Stage 2 might be the batteries for the 25-day beacon transmitter, for the Earth Return Orbiter to find it. MSFC says that keeping the batteries warm will use much of the battery energy (ouch, would RHUs make too much heat earlier in the mission?), but does not indicate required power or battery mass. The paper states that the Stage 2 burn "only exists to raise the periapsis," which seems like quite an understatement considering its share of the total delta V.

Around 460 kg (not shown in the table), a purely vertical launch is needed to reach 380 km, at which point the Stage 2 delta V would nearly equal orbital speed (with some help from planet rotation). Going straight up and then sideways is the least efficient path to orbit (other than zig-zagging around for no reason).

Risk areas in the MAV design
There is no indication whether it is easy or difficult to make the solid propellant burn about three times slower compared to STAR 20 motor heritage.

The authors point out a concern that the steering thrusters (RCS) are near the center of mass during the long coast between the Stage 1 and Stage 2 burns, which requires relatively larger RCS thrusters (hence more hydrazine). No information is included for the mass of RCS propellant, which effectively counts as Stage 1 hardware because it is mostly all there throughout the Stage 1 burn, and it is absent for the Stage 2 burn.

The paper describes multiple aerodynamic complexities that matter during the Stage 1 burn and during coasting, but then it is stated that flight testing above Earth will not include Stage 1.

As previously noted in Post #425, the paper says that the "trajectory and orbital performance is extremely sensitive to tip-off rates and vehicle pointing error during staging," while the Mars samples will result in an "unknown payload mass distribution." Hopefully there will be some way to know the sample masses or at least the sample tubes will be placed in a balanced configuration.

The MAV has gotten heavier with every design study, previous designs were deemed too heavy, and the latest design remains mostly "on paper." Therefore it might be a concern that mass growth is referred to euphemistically as a lack of "mass margin" and there is no discussion of the overall challenge presented by rocket performance fundamentals.

Coast time discrepancy
Trajectory simulations were initially expected to match the published coast time of "approximately 400 seconds," but this came out closer to 500 seconds. After some head scratching, the high school physics equation (distance equals half of acceleration times time squared) revealed that coasting 400 seconds upwards in Mars gravity (to a stop) would be about 300 km. Stage 1 burnout would need to be around 80 km altitude for the coast duration to be only 400 seconds up to 380 km. This discrepancy suggests that the published numbers might have lost something in translation or at least are not all finalized.

Regardless of the accuracy of all the published numbers, or whether I missed something, the MAV design paper is certainly a welcome progress report and it offers us much food for thought.

Attached File(s)

 MarsLaunchTable2022Apr15.pdf ( 129.7K ) Number of downloads: 155

 

[John Whitehead]

Attached is an older NASA plan for the part of the MSR mission that would land and retrieve the samples (now being collected by Perseverance), unknown to myself until very recently. The document was prepared in 2010 for the (then) Planetary Decadal Survey (2013-2022). The following summary is interesting to compare to the present ongoing (finally funded) MSR Campaign, which has been referred to as "focused and rapid" since 2018.

Key points from the April 2010 plan.
--The lander would carry both a fetch rover and a MAV (page 7 of the PDF).
--The new challenge is Mars ascent (PDF p 7-8 and 11).
--"The mass of the MAV is a key driver for landing a surface package on Mars" (PDF p 11).
--Two-stage solid propellant MAV, 300 kg, to a 500-km orbit (PDF p 21).
--Three-axis stabilized "to avoid issues with payload center-of-gravity variation and nutation" (PDF p 21).
--MAV launch would be a "critical event," so telemetry was required during and after flight (PDF p 21).
--MAV mass growth might cause redesign or rescope of the lander, but not likely (PDF p 27).
--Low likelihood that MAV development would be more difficult than planned (PDF p27).

Schedule as envisioned in 2010.
--MAV design studies start in 2011, propulsion system demo within three years (PDF p 11, 30-31).
--Further early technology development, then five years of MAV development, 2016 through 2020 (PDF p 30).
--Including early technology development, MAV work starts 7 years before mission PDR (PDF p 27, 30).
--Flight testing of the MAV at high altitude over Earth (PDF p 11, 21, 27, 30).
--Three flight tests, at least two successful flight tests required before mission PDR (PDF p 31).
--Mission PDR in mid-2020, MAV and fetch rover launch from Earth in late summer 2024 (PDF p 30).

Perspective from mid-2022 (see Post #433 for more details).
--MAV design studies were funded in 2011 (no testing), then the plan was delayed for almost a decade.
--As of circa 2020, there was only a 2-year change in Earth departure (2026 vs 2024).
--The three-axis stabilized MAV became heavy, leading to the spin-stabilized upper stage (nutation).
--No telemetry during upper stage critical events (spin-up, burn, and de-spin).
--The orbit altitude above Mars is less now.
--The less-heavy design became too heavy to include the fetch rover on the same lander.
--Building and testing the MAV is now starting, 6 years before Earth departure expected in 2028.
--Flight testing is only planned for the risky spinning upper stage, while previously the less risky MAV design was required to have two successful flight tests.

Attached File(s)

 Mattingly2010decadalMSRlander.pdf ( 2.95MB ) Number of downloads: 175

 

[stevesliva]

Good "presented without comment" summary, John. The good news is that when we know meeting the schedule seems implausible, we can always be happily surprised.