Author Topic: Skycrane future developments discussion thread  (Read 9169 times)

Offline Kaputnik

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Skycrane future developments discussion thread
« on: 02/27/2021 06:17 pm »
Please use this thread to discuss the EDL hardware and procedures used in the Curiosity and Perseverance missions, and to suggest improvements and how the system could be evolved.

I'll kick it off with this:

The descent stage will remain a one use vehicle for as long as there is no way of manufacturing hydrazine on Mars. Change my mind.
« Last Edit: 02/27/2021 06:17 pm by Kaputnik »
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Rocket Science

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I guess they could land tanker ships with drop tanks...
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Offline edzieba

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Re: Skycrane future developments discussion thread
« Reply #2 on: 02/28/2021 09:33 am »
Any mass put on the descent stage/skycrane is mass you've taken from the rover (the actual payload) mass budget. Landing legs, extra cameras, extra computers, extra propellant, etc. All of that mass is stolen from the object you actually want to land, in order to 'save' what is in effect a glorified parachute.

Offline Mader Levap

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Re: Skycrane future developments discussion thread
« Reply #3 on: 02/28/2021 12:19 pm »
There is nothing to improve, since completely different landing system is needed if we want to go beyond one scientific rover per 10 years.
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Offline Jim

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Re: Skycrane future developments discussion thread
« Reply #4 on: 02/28/2021 02:13 pm »

So, are you saying that a Descent Stage built more than 10 years ago was made in a way that cant be improved?

Yes, that is why they reused the DTM Descent Stage.  There was little improvement to be done by building a new using lessons learned.


That it's impossible to design today a Descent Stage with the same T / W, even using the same engines if you will, but carrying more equipment to provide a controllable soft landing?


Correct.  There is no room in the same 15 foot diameter aeroshell to add more propellant and still fly the same size rover.  If more propellant is to be reserved for landing the descent stage and more mass added to the descent stage, then mass has yo be removed from the rover.


I know it can. And that's why we are saying that looking to a future project with the mind in an old one is not what was pointed out here.


No, you don't.    The Mars 2020 rover and descent stage are a fixed mass system and are constrained by the volume of the Mars 20210 15 foot diameter aeroshell and the Mars 2020 parachute system.  No more mass can be delivered to the surface of Mars using the Mars 2020 hardware.  I specifically listed Mars 2020 everywhere because that is what we are talking about.  I am not talking about using the skycrane maneuver on a future mission with a different launch vehicle, different aeroshell and different spacecraft.  It is impossible to modified the Mars 2020 descent stage to allow it to land without taking mass from the rover using the same aeroshell.

And yes, we are talking about flying hardware, in an atmosphere, with gravity. So the Descent Stage it's not a spacecraft, it's more an aircraft than a spacecraft. With different variables, but with the same principles.

You could not be more wrong.  The descent stage is a spacecraft much like the Apollo Lunar Module and it is far from an aircraft.   Aerodynamics play no role in its operation.  The rocket equation rules everything with its operation.  Aerodynamics play a role during the entry and the parachute portion of the mission.  But once the Powered Descent Vehicle (PDV) is released from the backshell, it is all rocket propulsion and no aerodynamic.  The descent stage doesn't even have aerosufaces.  And it fails to mean the definition of an aircraft "An aircraft is a vehicle that is able to fly by gaining support from the air.".  Nope, all rocket propulsion.

And we will see another one performing a Skycrane maneuver, for sure.


You have nothing to base that statement on.  Nothing, no inside knowledge, no professional knowledge, no even educated guess.


Anyways, I'm convinced that, for some reason, it's impossible to debate here. It's more like a "convince Jim" thread than a Perseverance thread. I prefer not to play that game.

It isn't impossible to debate here.  It is just impossible to post statements that are not defendable without getting called on it.


« Last Edit: 02/28/2021 03:08 pm by Jim »

Offline Jim

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Re: Skycrane future developments discussion thread
« Reply #5 on: 02/28/2021 03:28 pm »
Visual aids

The rover and descent stage which are in the green rectangle and are constrained by the volume of the aeroshell (A & B) and the mass braking ability of the aeroshell and the parachute (in the container designated by the arrow).

Offline Stan-1967

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Re: Skycrane future developments discussion thread
« Reply #6 on: 02/28/2021 04:02 pm »
This discussion spun off from the aesthetic insult some contributors felt about the descent stage crashing. 

My aesthetics are more interested in the potential for mass to be shaved off any future descent element so more instruments can be included on the rover/payload portion.

From what information I could find,  it seems like the fly away descent element is throttled pretty low when landing.  The 8 engines and structure seem pretty beefy and overpowered.  This makes sense for the first efforts with Curiousity & Perseverence,  but what now?   

What lessons have been learned that may contribute better mass efficiency to future mission like sample return or prepositioned equipment for human exploration?


Offline Kaputnik

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Re: Skycrane future developments discussion thread
« Reply #7 on: 02/28/2021 04:42 pm »
Is the "throttled down" observation maybe related to the ability to have engine-out capability on the descent stage?
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Jim

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Re: Skycrane future developments discussion thread
« Reply #8 on: 02/28/2021 05:25 pm »

From what information I could find,  it seems like the fly away descent element is throttled pretty low when landing.  The 8 engines and structure seem pretty beefy and overpowered.  This makes sense for the first efforts with Curiousity & Perseverence,  but what now?   

What lessons have been learned that may contribute better mass efficiency to future mission like sample return or prepositioned equipment for human exploration?


This is only for rovers and not sample return.

Offline libra

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Re: Skycrane future developments discussion thread
« Reply #9 on: 02/28/2021 06:00 pm »
The attached paper explain why and how we are trapped with the present EDL system, harcking back to Viking 45 years ago.
Every single parameter is on the edge of present state-of-the-art / tech.

A lot, if not all, parameters are heavily stacked against Mars E-D-L systems.

- aeroshell diameter, because shrouds, because rockets diameter

- parachute / skycrane / retrorocket landing sequence

- Mars, its atmosphere, and its landscape.

It is an excellent reading, even if 15 years old. Not that far away since they were preparing Curiosity back then, and Mars 2020 is an improved variant of it.

One example of a damning EDL parameter: Mars landscape. The volcanoes and their "bulge", compared to Mars as a whole, are so huge - one half of the planet is 3 to 5 km, average, higher than the other one.
As far as present E-D-L systems go, that difference amounts to the difference between a successfull gentle landing and a Mach 3 crash right into Mars solid ground.

The atmosphere, too, is a [female dog, rude word] with seasonal fluctuations of its thickness, and its difficulty to fill a parachute even at Mach 2 or more.

Plenty of things like that, the paper explains extremely well.

Offline Stan-1967

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Re: Skycrane future developments discussion thread
« Reply #10 on: 02/28/2021 09:20 pm »
Thanks for linking the IEEE paper.  It states much of what I think Jim was holding back on, & he may know even more recent directions of what paths for Mars EDL are currently favored.  For certain advancements have been made in the area of making  retropropulsion & HIAD devices viable for heavier payloads.

It seems like Mars exploration is a pivot point where the current EDL using the Descent Element+ Skycrane maneuver is very close, if not already over.  ( at least for USA & ESA missions, no idea about China's intent) 

Concepts for the sample retrieval rover & sample return look to perform EDL within the current constraints on aeroshell size, but will land more like Viking or Pathfinder Phoenix.  Beyond that, there are no planned missions with the possible exception of the astrobiology laboratory.  Whatever comes after these missions, if anything, will probably depend on how interesting Mars is for science & human exploration. 

Skycrane, as currently constrained, seems completely inadequate for any human exploration needs.  If Perseverance or any other missions fail in finding compelling biosignatures, I could see the scientific community lose interest in prioritizing Mars & move on to Europa, Enceladus, & Titan.  If any of them do find biosignatures, Skycrane type delivery of payloads to the surface still look to be inadequate & will be surpassed by newer methods.


edited per Jim's note below.  Mars Pathfinder used airbags, my recollection was incorrect.   I was thinking of the Phoenix lander.
« Last Edit: 02/28/2021 09:49 pm by Stan-1967 »

Offline Jim

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Re: Skycrane future developments discussion thread
« Reply #11 on: 02/28/2021 09:32 pm »
, but will land more like Viking or Pathfinder.


Not like Pathfinder ever again

Offline Stan-1967

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Re: Skycrane future developments discussion thread
« Reply #12 on: 02/28/2021 09:53 pm »
, but will land more like Viking or Pathfinder.


Not like Pathfinder ever again

Jim's memory is better than mine.  I meant to say "Phoenix" lander, not Pathfinder. 

At least I didn't suggest we land via the method of Mars Polar Lander

Online Blackstar

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Re: Skycrane future developments discussion thread
« Reply #13 on: 02/28/2021 10:11 pm »
Jim's memory is better than mine.  I meant to say "Phoenix" lander, not Pathfinder. 

At least I didn't suggest we land via the method of Mars Polar Lander

MPL and Phoenix and InSight all used the same lander hardware.

Offline Cherokee43v6

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Re: Skycrane future developments discussion thread
« Reply #14 on: 02/28/2021 10:32 pm »
One thing I've seen mentioned from time to time on these forums is an ISRU Hopper.

I could see the Skycrane's thrust structure being used as the basis for such a lander, with the ISRU package depended below, giving the structure the necessary ground clearance for repeated takeoff and landing cycles.

Of course it would require a complete redesign of the rocket motors since they are currently hypergolics rather than an ignited mixture such as metholox that is the most commonly mentioned ISRU fuel.
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Offline Stan-1967

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Re: Skycrane future developments discussion thread
« Reply #15 on: 02/28/2021 10:35 pm »
Jim's memory is better than mine.  I meant to say "Phoenix" lander, not Pathfinder. 

At least I didn't suggest we land via the method of Mars Polar Lander

MPL and Phoenix and InSight all used the same lander hardware.

I was more referring to the part where MPL had a high velocity event with the surface of Mars.  :) 

Offline LouScheffer

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Re: Skycrane future developments discussion thread
« Reply #16 on: 02/28/2021 11:38 pm »
It is impossible to modified the Mars 2020 descent stage to allow it to land without taking mass from the rover using the same aeroshell.
I too agree that modifying the descent stage for a soft landing is not particularly useful.

However, it's certainly not impossible.  JPL made a number of tradeoffs, sensibly in my mind, gaining simplicity but sacrificing performance.  These could be made otherwise to gain margin to land the descent stage.

First, could you squeeze more fuel in the descent stage?  There is certainly room (see below).  Then how about mass margin?   Currently the descent stage uses pyro valves to keep propellant from moving from tank to tank until the final descent.  It also uses ejecting masses (about 300 kg of them) to move the center of gravity off center, then center it again later in the descent.  Instead, JPL could use the pressurization sequence to move liquid fuel from tank to tank, changing the center of gravity, then move it back again.  This would reduce the needed ejectable masses, directly increasing the mass margin.  But it's extra complexity in an already complex sequence.

More generally, JPL chose a monopropellant for simplicity.  A bi-propellant descent stage would only need 300 kg of propellant as opposed to the 400 kg they used.  (Plus the tanks would be lighter both due to smaller size and lower pressure - most biprop engines work at 20 bar, as opposed to the 46 bar of the JPL engines.)  This would leave plenty of margin to land the descent stage.

Finally, their descent profile is designed to be as safe as possible, not to use the minimum fuel.   A more hoverslam-type landing would use less fuel, leaving more for post-rover-dropoff maneuvers. 

Once again, I don't think these changes are a good idea.  But there is certainly slack in the system - the descent stage had reliability in mind, not the utmost possible performance.   As a side effect of this philosophy, the performance could be increased by modifications, if there was a need.

Offline Vultur

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Re: Skycrane future developments discussion thread
« Reply #17 on: 02/28/2021 11:45 pm »
Whatever comes after these missions, if anything, will probably depend on how interesting Mars is for science & human exploration. 

And what happens with SpaceX's plans...

Quote
If Perseverance or any other missions fail in finding compelling biosignatures, I could see the scientific community lose interest in prioritizing Mars & move on to Europa, Enceladus, & Titan.

Well - if they remain limited to current mission types, possibly yes. But I think if human missions to Mars are happening, bringing those scientific payloads along (small mass in comparison) would be a lot cheaper & would keep happening.

I think what happens with Mars science post-Perseverance will be determined by whether SpaceX's human Mars plans succeed or fail.

Offline Stan-1967

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Re: Skycrane future developments discussion thread
« Reply #18 on: 03/01/2021 12:19 am »

And what happens with SpaceX's plans...


Well - if they remain limited to current mission types, possibly yes. But I think if human missions to Mars are happening, bringing those scientific payloads along (small mass in comparison) would be a lot cheaper & would keep happening.

I think what happens with Mars science post-Perseverance will be determined by whether SpaceX's human Mars plans succeed or fail.

SpaceX's plans are irrelevant to any future Skycrane developments.

I think your point may be retro-propulsive landings will obsolete everything else.  Maybe...maybe not...that is a possibility, however current missions like sample return are paced towards later this decade.  Even if SpaceX succeeded with landing on Mars tomorrow, nothing is in the NASA, ESA, JAXA or any other agencies pipeline for science missions that would take advantage of that.  ( I could be unaware of it , but haven't heard of anything)

Offline AstroWare

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Re: Skycrane future developments discussion thread
« Reply #19 on: 03/01/2021 12:35 am »
Whatever comes after these missions, if anything, will probably depend on how interesting Mars is for science & human exploration. 

And what happens with SpaceX's plans...

Quote
If Perseverance or any other missions fail in finding compelling biosignatures, I could see the scientific community lose interest in prioritizing Mars & move on to Europa, Enceladus, & Titan.

Well - if they remain limited to current mission types, possibly yes. But I think if human missions to Mars are happening, bringing those scientific payloads along (small mass in comparison) would be a lot cheaper & would keep happening.

I think what happens with Mars science post-Perseverance will be determined by whether SpaceX's human Mars plans succeed or fail.
I think there is a possible future where human missions (like SpaceX, but not exclusively) and robotic missions like Perserverence can work together.

Planetary protection issues: if nasa wants pristine samples from special areas, a Rover, sent direct to the zone is preferred. Perserverence is this kind of system.

Sample return: as nasa sample return mission architecture shows, there is a high cost per kilogram returned to earth. That is where manned missions can help. Picking up curated samples from designated caches. This would only constitute a small piece of the manned mission but huge scientific reward.

Rovers like Percy can be sent ahead of manned missions to collect samples before possible contamination. But beyond that, There is Prospecting. If orbital surveys are sufficient to prospect landing sites, that's great. But it's a big risk too. Ground truth measurements from Landers could bring down that risk prior to human missions.

All this is to say -
In this future I think further use and development of the skycrane system is worthwhile, even in a future with starship.

 

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