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kbd512

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Registered: 2015-01-02

Posts: 7,856

Advanced Mars EDL Technologies for Manned and Unmanned Missions

As the title of this thread suggests, we're here to discuss technologies that improve our landed tonnage per unit mass of propellant expended.  While propulsive landings permit any tonnage to be landed for which sufficient propellant can be expended, even when combined with other EDL technologies like expandable or inflatable aerodynamic decelerators, propulsive landings require a rough 50/50 split between EDL hardware and payload for payload masses over 1t.  With propellants that provide substantially better specific impulse, such as LOX/LH2, it is possible to improve on that a bit.  However, any EDL solution that makes substantial use of retro-propulsion will ensure that a substantial percentage of the tonnage sent to Mars will be EDL hardware.

Unfortunately for us, Mars is a particularly challenging EDL environment.  Let's review NASA's MSL mission to illustrate just how challenging it is:

Reentry occurs at roughly 125 km in altitude above the surface of Mars at a velocity of more than 5.8km/s.  Peak heating is up to 2100C over certain areas of the heat shield, largely due to flow turbulence.  Peak deceleration is 12.9G.  The heat shield is subjected to almost 48t of compressive and shear loads, generating considerable deflection under load.  The supersonic parachute generates a peak drag force of more than 29t.  All that pushing and pulling on the reentry vehicle and payload generates pretty extreme performance requirements.

The reentry vehicle mass is 2455 kg and 899 kg of payload is landed.  That's 73% EDL hardware and 27% payload.  The problem is even more severe when we consider the fact that 530t worth of aerospace hardware was required to deliver that payload.  Landed payload mass works out to just .17% of the mass required to deliver it.  That's pretty poor by any standard.

While there are other things we certainly can and should do to improve the mass fraction of the payload with respect to the propulsion system mass required to deliver it, here we're going to focus on what we can do to substantially reduce the mass of the EDL hardware.  Whatever the ultimate solution is, resolution of this issue is on the critical path for human exploration of Mars.

There are three basic aerodynamic deceleration technologies we can work with:

1. Ballons

Pros:

Assists with deceleration

Can be quite light and can contain light gases like hydrogen and helium

Fabrication is straightforward and well understood

Cons:

Requires advanced materials to survive heating associated with reentry

Likely difficult to make precision landings with

Requires a rapid inflation deployment mechanism

2. Parachutes

Pros:

Assists with deceleration

Even lighter than a ballon

Fabrication is straightforward and well understood

Cons:

Requires advanced materials to survive hypersonic deployment

Likely difficult to make precision landings with

Requires a forced inflation deployment mechanism for any substantial payload

3. Wings

Pros:

Creates aerodynamic lift

Control surfaces make precision landings possible

Potentially provides the most complete solution, from reentry to just before touchdown

Cons:

Fabrication requires advanced materials for sizes relevant to landing any substantial payload

Occupies a much larger physical volume than a ballon or parachute for sizes relevant to landing any substantial payload

Requires extensive aerodynamic testing to assess performance

SpaceNut

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From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

Simular to the wing is just to increase the diameter of the heatshield
after that its just fuel and engines to perform retropropulsion

tahanson43206

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Registered: 2018-04-27

Posts: 19,406

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

For kbd512 .... Thanks for starting this topic. 

I had to look up EDL (to be more sure rather than just guessing), so for others who might wonder
Per NASA web site EDL = Entry, Descent, and Landing Technologies

For SpaceNut re #2 ... Your suggestion calls for computer modeling, so I hope that a forum reader with the appropriate software will run some simulations. The wispy nature of the Mars atmosphere would appear to be a challenge for any landing technology dependent upon it.

For a change of thinking .... There has been extensive discussion in the past year of the use of tethers anchored to Phobos to allow landing craft to gently descend into the Martian atmosphere.  The hard work of decelerating after a trip from Earth would have been accomplished if the payload/vessel has already matched orbit with Phobos.

And ** that ** leads me to offer the observation that it was recently proposed in another topic, to employ a very common technique for catching fish on Earth, to the problem of matching orbit with Phobos.

A fishing technique known to and practiced by many, is to let a line into a body of water in such a way as to attract a fish.  Often, in open ocean settings, the fish which accepts the bait or other attractive element is heavier and stronger than the line can hold.  The operator of the fishing equipment allows the line to pay out against resistance, to tire the fish, always taking care to keep the tension on the line well under its maximum strength.

While the engineering challenges are daunting, the same principle could be applied in capturing incoming vessels arriving at Phobos, or with reference to Calliban's topic about asteroids, could be applied to capturing asteroids.

In both cases, whatever differences in momentum and vector exist between a given object and a vessel intending to capture it could be (in principle) managed by appropriate operation of the line management subsystem.

(th)

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

The edl is made complex for mars as what it has for an atmospher is not zero but then again its not all that much with a density that changes with the season and day to night landings as well. Things that we also know is the size of the parachutes are sort of at max diameter for the mass we are delivering such that we are not going to make them any larger to support the larger payloads that we need.

Conceptual Modeling and Analysis of Drag-Augmented Supersonic Retropropulsion for Application in Mars Entry, Descent, and Landing Vehicles
https://scholar.colorado.edu/cgi/viewco … n_gradetds

Guidance, Navigation, and Control System Performance Trades for Mars Pinpoint Landing
https://engineering.purdue.edu/~mjgrant … -and-2.pdf

STRATEGIES FOR MARS NETWORK SCIENCE MISSIONS VIA INNOVATIVE AEROCAPTURE AND EDL ARCHITECTURES
https://engineering.purdue.edu/RDSL/ipp … --june.pdf

Atmospheric Environments for Entry, Descent and Landing (EDL)
https://ntrs.nasa.gov/archive/nasa/casi … 032693.pdf

Mars Entry, Descent, and Landing Trajectory and Atmosphere Reconstruction
http://www.ssdl.gatech.edu/sites/defaul … S-8900.pdf

tahanson43206

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Registered: 2018-04-27

Posts: 19,406

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

For SpaceNut re #4 and specifically the Masters Thesis from Colorado University.

The objective of this thesis is to perform a systems architecture study of peripheral
nozzle supersonic retropropulsion technology for use in Mars entry, descent, and landing
vehicles. Peripheral nozzle SRP currently lacks simple analytical tools suitable for a systems
level study to determine whether its drag preservation characteristics can be utilized to make
SRP more efficient. This research focuses upon the following analysis areas:

The first part of this paper reviews prior art, including Soviet and American attempts.

At one point the author explains the limit on aeroshell size ... the size of the upper stage of the launch vehicle.

Earlier (I believe in this topic) you observed that it might be possible to use a very large aeroshell to fly through the Mars Atmosphere.

While the limitation of the diameter of the launch vehicle will extend into the foreseeable future, I do NOT think it is necessary to accept that limitation as binding on future vehicles intended for landing on Mars.  Large aeroshells could be assembled in Low Earth Orbit using sections delivered to orbit by existing vehicles.

The heat shield could be applied in space, if it is not already bonded to the sections.

(th)

SpaceNut

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From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

There is also the nasa work on HIAD, ADEPT, Hypercone and a few more technologies as it relates to making a larger heat shield from a small closed up package which include inflateables.

Testing is part of the tech but sensing is the other so as to be able to prove out the conditions that math and testing tell you what you need to use and how much of it for materials that can take the heat.

https://www.nasa.gov/centers/ames/therm … /stmd.html

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Advanced Mars EDL Technologies for Manned and Unmanned Missions

Slides & animations from Starship 2019 update presentation by Elon Musk

SpaceX Starship interior concept for 100 passengers