Landing a flying saucer on Mars

GW Johnson · 2014-04-20 13:16:45

Folks have made a big deal out of lighting a rocket engine whose nozzle faces into a supersonic or low-hypersonic slipstream. That might be an issue with Earth entry (not proven either way yet), but I doubt it's that much of an issue on Mars. That's because the densities and velocities are so much lower during entry there. That means dynamic and pitot ram pressures are also a lot lower.

The cant angle solves the reversing-stream stability issue that otherwise could potentially lead to attitude control loss, if your attitude thrusters are weak. Spacex's 45 degree cant for the (not weak at all) Super Dracos is driven by geometry, not plume stability. They are firing from pods mounted on the afterbody, not anywhere on the windward-facing heat shield. It takes about 45 degrees from a low afterbody position to clear the rounded corner of the heatshield without a hot plume strike on that heat shield.

There's no data to support or deny this, but my engineering intuition suggests that 10 to 15 degrees of cant would more than suffice to ensure plume stability for supersonic retropropulsion. That remains to be seen in testing, but could be verified in flight at about 100,000 feet right here at home.

The remaining question is how many engines and where in the heat shield do you put them? Opinions vary. I'd guess 4 to 8, nearer the center to restrict engine-out torque transients that might destabilize attitude. Others prefer a ring nearer the outer perimeter of the heat shield. My guess is that either, or anything in between, could be made to work. Something else will constrain that choice.

Do these need ports through the heat shield with doors that close when the engines are not firing? Again, opinions vary. I'd say that no, doors are not necessary, if-and-only-if you can reliably seal the engine compartment to prevent all throughflow. There is no better insulator than a static gas column, even against entry plasma.

All of this is easily tested for basic feasibility by models shot to 100,000 ft on balloons and/or sounding rockets. You can shoot higher and turn nose-down and thrust again to achieve very hypersonic speeds as you hit 100,000 feet. We first did that with the X-17 ca. 1960. It works fine. Viking's chutes were tested that way, too, in the early 1970's.

Once you have a design known to be feasible, you build it, stick it on a bigger rocket, and test it "for real" all at once, at that same 100,000 feet where the density matches lower-altitude densities on Mars.

This is all very doable. Any outfit serious about landing big things on Mars would already be working on these things. NASA is generally not very serious about it yet, but Spacex is. Their Dragon with the Super Dracos and some legs is already proposed for one-way unmanned payloads over a ton for Mars, including the sample return mission.

GW

Quaoar · 2014-04-20 14:43:43

GW Johnson wrote:

There's no data to support or deny this, but my engineering intuition suggests that 10 to 15 degrees of cant would more than suffice to ensure plume stability for supersonic retropropulsion. That remains to be seen in testing, but could be verified in flight at about 100,000 feet right here at home.

I think you are right. If you put the rokets nearer the outer perimeter, is it possible to have them fire perfectly vertical and let the atmospheric flow cant the plumes outward douring descent?

GW Johnson wrote:

The remaining question is how many engines and where in the heat shield do you put them? Opinions vary. I'd guess 4 to 8, nearer the center to restrict engine-out torque transients that might destabilize attitude. Others prefer a ring nearer the outer perimeter of the heat shield. My guess is that either, or anything in between, could be made to work. Something else will constrain that choice.
Do these need ports through the heat shield with doors that close when the engines are not firing? Again, opinions vary. I'd say that no, doors are not necessary, if-and-only-if you can reliably seal the engine compartment to prevent all throughflow. There is no better insulator than a static gas column, even against entry plasma.

A question about your landing boat design: do the nozzles open in fixed holes in the center of the heatshell, or in a bigger sealed compartment where they are free to pivoting for thrust vectoring control?

Last edited by Quaoar (2014-04-21 05:16:52)

GW Johnson · 2014-04-21 09:16:31

Hi Quaoar:

On my landing boat design, I had 4 engines near the center, inside a room sealed to the backside of the heat shield structure. That design would only need to gimbal a little in the engine-out condition, where only two diametrically opposite are running. Or you could rely on attitude control thrusters for steering (as in the 1960's-vintage Scout launcher).

With all 4 engines running, differential thrust among the engines will provide steering about as well as gimballing would. For engines nearer the periphery, the differential thrust moment is even larger, but so is the disturbing moment when one engine quits, but before you can shut the diametrically-opposite one down to compensate. So, maybe 8 smaller engines is even better. I don't know, really.

As for off-center but axially-oriented engines having stable plumes, I don't know. I'd cant around 10 degrees in a first design, just to be sure. Cosine(10 deg) is a number fairly close to unity, so there's not any really significant loss of thrust and Isp at low cant like that. It'll take some flight experience with this, in more than one vehicle, to really know the art of doing it.

GW

Last edited by GW Johnson (2014-04-21 09:19:21)

Quaoar · 2014-04-24 09:47:35

GW Johnson wrote:

Hi Quaoar:
On my landing boat design, I had 4 engines near the center, inside a room sealed to the backside of the heat shield structure. That design would only need to gimbal a little in the engine-out condition, where only two diametrically opposite are running. Or you could rely on attitude control thrusters for steering (as in the 1960's-vintage Scout launcher).
With all 4 engines running, differential thrust among the engines will provide steering about as well as gimballing would. For engines nearer the periphery, the differential thrust moment is even larger, but so is the disturbing moment when one engine quits, but before you can shut the diametrically-opposite one down to compensate. So, maybe 8 smaller engines is even better. I don't know, really.
As for off-center but axially-oriented engines having stable plumes, I don't know. I'd cant around 10 degrees in a first design, just to be sure. Cosine(10 deg) is a number fairly close to unity, so there's not any really significant loss of thrust and Isp at low cant like that. It'll take some flight experience with this, in more than one vehicle, to really know the art of doing it.
GW

Your landing boat has 4 rocket: let's call them R1, R2, R3, and R4: in case of R3 out, we have to shut down R1 or we can pivoting it to align its thrust to the center of mass and run with three rockets?

GW Johnson · 2014-04-24 15:47:16

Not much gimbal is needed for a near-center cluster, when running on 3 out of 4. You just gimbal the odd one to thrust through the center of gravity. For a near-center cluster location, that's not a big angle. For a periphery location, it's really big.

But, with 4 engines, and you lose one, just run on 2 diametrically opposed, instead of 3. Differential thrust provides in-plane vector. Attitude control thruster provide out-of-plane control. No gimballing required.

But, my landing boat was just a rough-out design sizing. I never worked out the numbers in detail for engine-out.

GW

SpaceNut · 2014-05-19 17:36:03

Bumping the topic

SpaceNut · 2015-03-29 22:04:51

Low-Density Supersonic Decelerator Project (LDSD) NASA’s “flying saucer” prepares for another spin

The 7,000 lb (3,175 kg), 15-foot (five meter) wide, test vehicle is currently being prepared for shipment to Hawaii in a clean room at NASA’s Jet Propulsion Laboratory (JPL ) in Pasadena, California.

The goal of the LDSD mission is to test new technologies that allow large payloads to be safely landed on Mars and other planetary bodies with atmospheres.
The LDSD program is testing and developing three new deceleration devices. With the space agency planning on sending crews to the Red Planet as early as sometime in the 2030s, having a light-weight method of atmospheric reentry is critical to its efforts.

Here we go again decades later...

SpaceNut · 2015-09-07 15:21:41

Updating topic.....

RGClark wrote:

I suppose this should be in the thread discussing lightweight heat shields/decelerators for Mars but here is an another example, HIAD (Hypersonic Inflatable Aerodynamic Decelerators):

NASA Podcasts
NASA X: IRVE-3 1.30.13
Dr. Cheatwood: This concept would be coming back from the station, so entering at 7 1/2 kilometers a second, just like we were talking about at Mars. It would be bringing in anywhere from 3 1/2 to 5 metric tons, just like we were talking about at Mars. It would be between 8 and 10 meters in diameter, that actual HIAD, just like we were talking about at Mars. And we'll see heating of 25, 30, maybe higher, 35, 40 watts. So it's a very similar environment to Mars for that application. So we can do this flight test from the station for a very reasonable cost, and it demonstrates an ability to bring larger volumes and masses down from the station than we currently have, and it demonstrates that we could do this mission at Mars.
Pulley: With a successful heart mission researchers feel that they may have enough information and knowledge to proceed for the ultimate goal, which would mean seeing a HIAD at Mars.
Dr. Cheatwood: I believe in the technology. And, you know, I think, you know, if somebody wanted to give me a budget and say, "get us to Mars with humans in 2020," I think we could get there on this technology. I can't speak for other technologies. But no, I think we could get there.
http://www.nasa.gov/multimedia/podcasti … -0103.html
This is the transcript of this video:
NASA 360 | Hypersonic Inflatable Aerodynamic Decelerators (HIAD) [HD].
http://www.youtube.com/watch?v=hJUd3zanD8k
While I appreciate these inflatable heat shields allow you to get heavier mass to Mars, I've never seen any architecture for a manned Mars missions that only required to get 5 metric tons to the Martian surface.
Bob Clark

SpaceNut · 2015-09-07 15:23:10

GW Johnson wrote:

7 km/s entry at Mars seems high. Isn't 5 km/s closer to the "typical" direct interplanetary transfer entry?
If you can guess a hypersonic drag coefficient for the inflatable-or-extendable fabric heat shield shape (somewhere in the 1.4 to 1.7 range), and you have accurate figures for both entry speed and entry trajectory angle below horizontal, the old Julian Allen warhead entry analysis I use does a decent ballpark job telling you peak gees, peak heating, and end-of-hypersonics (about local Mach 3). You'll have those quantities plus the altitudes and speeds at which they occur.
Peak decel gees and heat shield diameter, coupled with density at peak gee altitude, give you the average pressure exerted over the heat shield. You can figure stagnation pressure pretty easily, and your average ought to be between stagnation and nothing, probably about half stagnation as a ballpark guess. You can even guess a pressure distribution from that.
The pressure distribution and geometry lead you to structural stress/strain analysis. The pressure distribution and geometry also lead you to a ballpark estimate of gas leakage due to porosity. That and the old rule of thumb that gas temperature in deg K is speed in m/s divided by 10, gives you a shot at a ballpark heat transfer analysis.
I'd be very wary of impregnating the fabric heat shield with any resins. You lose flexibility and impact damage resistance that way. If you need to impregnate it, use an elastomer. I'd go with a hard char-forming solids-doped silicone, myself. Probably not exactly DC-93-104, but something like it.
None of that takes any account of factor-2+ variability in the high altitude density profile at Mars, something that does not happen here. Your end of hypersonics point will vary exponentially with things like that.
Most of the ballistic coefficient stuff I have done recently suggests that ballistic coefficients are larger at larger vehicle masses, shapes and proportions being otherwise unchanged. It's a square-cube law thing. When those get too big, on Mars chutes get to be quite useless post-hypersonics. The way out of that dilemma is supersonic retropropulsion technology. There'll be a point where square-cube scaling won't let you build a survivable inflatable/extendable heat shield for vehicles that large.
My own studies are not for a minimalist mission, but more like a mission with an orbital transport and multiple landers. Those landers typically exceed 30 tons, and approach 100 tons, depending upon propulsion choice and payload size. Their ballistic coefficients typically fall in the 300-500 kg/sq.m range. The probe folks at JPL seem to need Rube Goldberg stuff above about 100 kg/sq.m. So, that's the "breakpoint" where you start needing to use supersonic retropropulsion instead of chutes.
The inflatable/extendable heat shield is a way to reduce ballistic coefficients at larger vehicle mass. But, you will hit that 100 kg/sq.m limit rather quickly, even with heat shields like that. I rather doubt a 5 ton lander would be very useful.
GW

SpaceNut · 2015-09-07 15:26:03

kbd512 wrote:

No matter how small, development and testing of altimeter triggered retrorockets that work perfectly, every time, on another planet is sure to be insanely expensive. If there's a simpler and less expensive option to successfully complete EDL for humans, then that's what we should work on until the Orion and SLS spending projects are over. Once we've blown enough cash on those two projects without meaningful result or someone at NASA grows a pair and says what needs to be said to the morons in Congress, then we can develop two stage multi-person landers that can return to the MTV if they land substantially off-course.
At no time have I thought that my solution was in any way optimal, but a $3B total outlay over six years is eminently reasonable compared to the alternatives. Any multi-person lander with contingency supplies that includes a fully fueled ascent vehicle is far, far preferable to my solution.
If we have reasonably priced and fully tested EDL solutions for humans (HIAD + Parachute) and cargo (ADEPT + retro-propulsion), I think we stand a far better chance of going to Mars than if there was no solution because we had to wait ten or more years for funding availability. ADEPT and retro-propulsion are a little further away than HIAD and parachutes; just far enough that I think two separate approaches to solving the problem is appropriate.
Even in the Martian atmosphere, I have a hard time believing that we would not achieve a substantial reduction in velocity before touchdown with a payload that's less than half the mass of Pathfinder, using the same size/type parachute, and an inflatable aeroshell capable of generating more lift than the rigid aeroshells used by Pathfinder and MSL. We may still need some sort of airbag to absorb the impact on touchdown, but if it's possible to only use HIAD and a parachute, that's the way to go.
I am submitting a request for MarsGRAM data to NASA so that I or someone else can determine what the feasibility of soft landing 150kg or less without retro-propulsion would be.

SpaceNut · 2015-09-07 15:43:11

I am always surprized when I find out that the research for what we are talking about is just right next door so to speak.
UMaine engineers working with NASA on space technology

University of Maine engineers are starting their third year of research funded by NASA on a device that could help carry cargo, or even humans to Mars.
The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) is a device that will be made out of inflatable fabric material braided together that can help slow down a large spaceship carrying scientific equipment or astronauts.
With the thin Mars atmosphere, NASA is trying to find a way to slow spacecrafts down to avoid damage from crashing on the planet’s surface. Bill Davids, chair of the UMaine Civil and Environmental Engineering Department and the John C. Bridge Professor, have been overseeing the student testing portion of this research.
“We have made significant progress on developing novel test methods for these fabric structures,” Davids said. “Our work has given NASA critical information about the properties and performance of the materials and components that make up the HIAD, which they have fed into their design simulations.”
The department is using $750,000 from their four-year grant to investigate different materials that can be used for such a trip. According to Davids, the primary materials being tested have been synthetic polymers Vectran and Zylon.
Davids continued explaining that UMaine is mostly independently working with an aerospace company who is supplying them with inflatable structures and reinforcing cords for the project. UMaine engineers have also been collaborating with engineers from Georgia Tech. While research has been happening for three years, Davids said that there is still work to be done.

SpaceNut · 2016-03-27 08:48:28

We keep talking about the topics which we have here with the data to mine for how to solve the equation of getting to mars. This one is for landing large mass objects on its surface.....
and another is Adept....

I am surprized at how quickly our topics are buried into the past...

kbd512 · 2016-03-27 12:08:13

SpaceNut,

There's just not much in the way of fast-moving development in this area. If the goal is to actually land more massive payloads on Mars, then these projects have to be provided with more funding than they currently receive. Sooner or later, new EDL technologies have to be tested on Mars. To this day, the only EDL technologies that have seen use on Mars are all legacy technologies. The Mars 2020 rover is still set to use legacy technology. If indeed we are advancing the state-of-the-art in this required technology for landing humans on Mars, then we're doing it incredibly slowly. At the current pace of development, there's probably another five years worth of development before we see any EDL technology that is an improvement over current technology.

These EDL technology threads tend to get buried because the technology may as well be entirely theoretical until someone actually tests the technology in a realistic environment since Mars' atmosphere is so unlike Earth's atmosphere, the technical aspects of current EDL technology projects are buried in incomplete documentation, and apart from small demonstrators there's virtually no other use for these technologies.

If NASA decided to make more of the information related to these projects available to the general public, it's likely that aerospace engineers would find the problems interesting and contribute whatever they could reasonably contribute in their spare time to solving the problems.

SpaceNut · 2018-08-04 20:59:18

Been searching for the HIAD topic and surprise it was actually a couple of them ...
Hypersonic Inflatable Aerodynamic Decelerator

http://www.newmars.com/forums/viewtopic.php?id=5539

plus several pages in this one http://newmars.com/forums/viewtopic.php?id=6142

https://abcnews.go.com/Technology/nasa- … d=37518000

NASA's solution for helping a manned mission to Mars return safely to Earth looks like a giant inflatable donut, and it will serve as a crucial piece of technology helping to slow down a spacecraft as it enters the Martian atmosphere. A 9-foot diameter HIAD model made of Zylon and Teflon materials was tested using a vacuum pump, with engineers repeatedly checking it for potential damage, according to a NASA blog post. With that test successful, engineers now plan to create a larger HIAD that can be packed in a rocket and withstand extreme temperatures, such as those it may encounter when a spacecraft descends onto Mars.

https://www.nasa.gov/content/stmd-advan … h-to-mars/
Low Density Supersonic Decelerator

SpaceNut · 2018-08-12 08:59:38

https://cosmosmagazine.com/technology/h … craft-work

In the video below, you can see NASA testing a type of inflatable heat shield called the Low-Density Supersonic Decelerator (LDSD) for use in future Mars missions. The LDSD is covered in heat-resistant fibres and fabrics. This makes it suitable for decelerating craft at high speeds, but only for a short period of time. For more heat-intensive missions we need to examine another inflatable shield, also being developed by NASA.
https://youtu.be/9yRWhu0UGYw
Called the Hypersonic Inflatable Aerodynamic Decelerator (HIAD), it’s inflated just before re-entry and is designed to protect spacecraft headed to Mars.
A thermal protection system made from a concoction of advanced materials including Nextel, Pyrogen and Kapton provides heat shielding up to the 1,260 °C expected to be generated in the Martian atmosphere.
The strength to resist airspeeds as high as 42,000 kilometres per hour comes from inflatable rings made from braided Kevlar, a material normally found in bulletproof vests
A sample of the heat resistant material to be used on the HIAD shown here before testing. It can withstand over 1200 °C and speeds exceeding 40,000 kilometres an hour. – NASA
The whole shield can fit inside a bag around half a metre in diameter, which, when deployed, expands to more than six metres. This makes it far easier to package and can be popped in the nose of a rocket.
Click on the links to find out more about LDSD and HIAD, the next steps in heat shielding technology.

https://www.nasa.gov/mission_pages/tdm/ldsd/index.html

http://www.nasa.gov/directorates/spacet … yLBrKN96Rs

Quite the materials layering to make up the shield

SpaceNut · 2018-08-12 11:16:55

The key technologies include flexible TPS materials for hypersonic entry conditions, attachment and inflation mechanism and high-strength, lightweight, inflatable bladder materials capable of withstanding high temperatures to obtain a landing of heavy payloads (>20 metric tons) to Mars.

ippw2016.jhuapl.edu/docs/abstracts/combined-drag.pdf

https://ntrs.nasa.gov/archive/nasa/casi … 009113.pdf

https://ntrs.nasa.gov/archive/nasa/casi … 013167.pdf

SpaceNut · 2018-08-31 18:53:54

www.ssdl.gatech.edu/sites/default/files/papers/conferencePapers/AIAA-2016-0219.pdf
A High-Heritage Blunt-Body Entry, Descent, and Landing Concept for Human Mars Exploration

Human-scale landers require the delivery of much heavier payloads to the surface of Mars than is possible with entry, descent, and landing (EDL) approaches used to date. A conceptual design was developed for a 10 m diameter crewed Mars lander with an entry mass of ~75 t that could deliver ~28 t of useful landed mass (ULM) to a zero Mars areoid, or lower, elevation.
The EDL design centers upon use of a high ballistic coefficient blunt-body entry vehicle and throttled supersonic retro-propulsion (SRP). The design concept includes a 26 t Mars Ascent Vehicle (MAV) that could support a crew of 2 for ~24 days, a crew of 3 for ~16 days, or a crew of 4 for ~12 days.
The MAV concept is for a fully-fueled single-stage vehicle that utilizes a single pump-fed 250 kN engine using Mono-Methyl Hydrazine (MMH) and Mixed Oxides of Nitrogen (MON-25) propellants that would deliver the crew to a low Mars orbit (LMO) at the end of the surface mission. The MAV concept could potentially provide abort-to-orbit capability during much of the EDL profile in response to fault conditions and could accommodate return to orbit for cases where the MAV had no access to other Mars surface infrastructure. The design concept for the descent stage utilizes six 250 kN MMH/MON-25 engines that would have very high commonality with the MAV engine.
Analysis indicates that the MAV would require ~20 t of propellant (including residuals) and the descent stage would require ~21 t of propellant.
The addition of a 12 m diameter supersonic inflatable aerodynamic decelerator (SIAD), based on a proven flight design, was studied as an optional method to improve the ULM fraction, reducing the required descent propellant by ~4 t.

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#26 2014-04-20 13:16:45

Re: Landing a flying saucer on Mars

#27 2014-04-20 14:43:43

Re: Landing a flying saucer on Mars

#28 2014-04-21 09:16:31

Re: Landing a flying saucer on Mars

#29 2014-04-24 09:47:35

Re: Landing a flying saucer on Mars

#30 2014-04-24 15:47:16

Re: Landing a flying saucer on Mars

#31 2014-05-19 17:36:03

Re: Landing a flying saucer on Mars

#32 2015-03-29 22:04:51

Re: Landing a flying saucer on Mars

#33 2015-09-07 15:21:41

Re: Landing a flying saucer on Mars

#34 2015-09-07 15:23:10

Re: Landing a flying saucer on Mars

#35 2015-09-07 15:26:03

Re: Landing a flying saucer on Mars

#36 2015-09-07 15:43:11

Re: Landing a flying saucer on Mars

#37 2016-03-27 08:48:28

Re: Landing a flying saucer on Mars

#38 2016-03-27 12:08:13

Re: Landing a flying saucer on Mars

#39 2018-08-04 20:59:18

Re: Landing a flying saucer on Mars

#40 2018-08-12 08:59:38

Re: Landing a flying saucer on Mars

#41 2018-08-12 11:16:55

Re: Landing a flying saucer on Mars

#42 2018-08-31 18:53:54

Re: Landing a flying saucer on Mars

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