Smallest Human Ascent or Descent Lander for Mars Or Earth

SpaceNut · 2016-01-06 22:02:44

kbd512, do you have an image of the "reentry capsule that could be used multiple times on mars" as the first or initial entry speed given by GW is much higher than the ascent speed to which it would see for reuse.

MAD/MAV/Habitat is way to heavy to return to orbit and is a waste when the MTV is sitting in orbit waiting to bring the crew home. The only reason for a bigger MAV is to bring fuel up to the MTV if its designed that way otherwise it can be made smaller like in only slightly larger than the Red Dragon but then again that depends on crew size and return payload.....

Yes the MAD/MAV is used for such a small time its true but it must be the most robust piece as its just sitting on the surface waiting to be used for that one time to go home with. The very robust piece of equipment is the habitat which is already planned to have life support of the highest efficiency levels already and Nasa does plan to have rovers but then again how does that not force the EDL to be more advance on the other items used to land it.....

kbd512 · 2016-01-06 23:53:11

SpaceNut wrote:

kbd512, do you have an image of the "reentry capsule that could be used multiple times on mars" as the first or initial entry speed given by GW is much higher than the ascent speed to which it would see for reuse.

As previously stated, there is no spacecraft I am aware of that has survived reentry more than once without refurbishment.

A Curiosity style sky crane device could be equipped with landing gear. The sky crane device would be protected with a back shroud during reentry and attached to an ADEPT-equipped cargo container. The sky crane drops the cargo at a pre-determined altitude above the surface of Mars and the inverted ADEPT device serves as an impact cushion or soft lands the cargo at the expense of greater fuel consumption.

Instead of flying off and crashing a short distance away, the sky crane lands itself in a launch pit and a refueling robot inspects and refuels the sky crane from a methalox ISRU plant. The entire operation is autonomous.

The sky crane only needs landing gear strong enough to support its own weight, rather than its weight and the weight of the cargo.

The sky crane (rocket engines, fuel tanks, avionics) is reusable and constructed with field replaceable assemblies, but the reentry protection hardware is not.

SpaceNut wrote:

MAD/MAV/Habitat is way to heavy to return to orbit and is a waste when the MTV is sitting in orbit waiting to bring the crew home. The only reason for a bigger MAV is to bring fuel up to the MTV if its designed that way otherwise it can be made smaller like in only slightly larger than the Red Dragon but then again that depends on crew size and return payload.....

Apart from humans and sky cranes, anything landed on Mars stays on Mars. The MTV and the humans are the only things we're bringing back. Given the cost of the MTV, the MTV must be capable of returning with or without a crew. There's no reason to refuel the MTV at Mars when SEP tugs can transfer chemical kick stages from Earth to Mars.

My MTV uses a chemical kick stage to depart L1 and a chemical kick stage to depart LMO. Arrival at LMO and L1 are handled by spiraling in using SEP. That way, the mass of the kick stages stays within the launch capability of Falcon Heavy.

There are more moving parts using this solution, but the mass of each moving part is well within the launch capability of Falcon Heavy and the inevitable payload losses are not insanely expensive.

SpaceNut wrote:

Yes the MAD/MAV is used for such a small time its true but it must be the most robust piece as its just sitting on the surface waiting to be used for that one time to go home with. The very robust piece of equipment is the habitat which is already planned to have life support of the highest efficiency levels already and Nasa does plan to have rovers but then again how does that not force the EDL to be more advance on the other items used to land it.....

A sky crane could provide a multi-purpose solution for landing cargo and returning humans to the MTV, but it must be thoroughly tested on Mars before humans are strapped to it. My guess is that NASA will create entirely separate solutions for cargo and humans because it gives its contractors something to do.

GW Johnson · 2016-01-07 11:40:02

"No capsule flown more than once" -- actually, there was one, and there will soon be more.

One of the unmanned test Gemini capsules was re-flown unmanned for the one and only flight test of the USAF's MOL program in 1969. I do not know if they replaced or reused the heat shield, but the rest of the capsule was re-flown, at least. This one had a hatch cut through its heat shield, too, so that concept also works. That's the Gemini-B configuration required for access into the MOL from the capsule without going EVA. That very capsule is in a museum today.

The PICA-X heat shield sported by Dragon was designed to survive a free return re-entry from Mars. That means it's tough enough to survive two free returns from the moon, and several returns from LEO. Spacex has not yet chosen to re-fly an unrefurbished Dragon to LEO, but they could, and I believe that sooner or later they will. Why not? It'll work, and it lowers costs.

Entry at Mars is not as demanding as Earth entry, because the velocities are inherently lower there, unless you insist on a very high velocity direct entry. But we have the heat shield materials and design knowledge to survive that trip multiple times with a single heat shield "build".

If instead you choose to enter from LMO, it's so much less demanding that you can survive even stagnation-point heating on a blunt shape with low-density alumino-silicate refractories. No ablatives at all. If you can put some structural robustness into your application of those infamously-fragile materials, then there is the prospect of a craft which could make thousands, even tens-of-thousands of entries from LMO.

All of this is within our reach right now. You use those materials as a ceramic fabric-reinforced composite, not the simple low-density blocks that NASA did for shuttle. I did this myself over thirty years ago for an entirely-different application. Redundant retention is also key to a long-life design. But if you use the fabric reinforcement approach, then that very fabric offers a second way to attach your ceramic heat shield panel.

GW

kbd512 · 2016-01-07 16:39:37

GW,

It would be helpful to know whether or not any refurbishment activities beyond replacement of the heat shield occurred. I seriously doubt NASA would reuse a manned spacecraft without definitive test results to determine at what point the heat shield or other components would fail. That type of testing has a substantial price tag attached to it. More to the point, virtually every Mars vehicle lands on the heat shield or discards the heat shield after reentry to shed mass. Either way, any impact to the integrity of the heat shield has to be accounted for. For a propulsive landing, the propellant required to soft land the payload with the mass of the reentry hardware still attached also has to be factored into fuel consumption. If we can find a significant source of water on Mars, obtaining rocket fuel is easier. If not, any unnecessary fuel consumption should be weighed against the expensive and difficulty of shipping hydrogen to Mars.

SpaceNut · 2016-01-07 20:03:11

I saw today an article about 3D printing of ceramics which makes the heat shield now a replaceable item if damaged on Mars.

We have had other advances ain 3D printing capability and will also post thos there instead to keep the topic going on the Smallest Human Ascent or Descent Lander for Mars or Earth.

Based on numbers for the 2 destinations we have deverging designs and applications from the base plans as we have differing conditions for when the astronaut lands to contend with.

On Earth an astronaut is able to walk away from the landing site and go for any place within walking distance but on Mars the limitation is the space suits life support and the physical condition of the astronaut as you can only go as long as the space suit is working.....

kbd512 · 2016-01-07 21:44:35

SpaceNut wrote:

I saw today an article about 3D printing of ceramics which makes the heat shield now a replaceable item if damaged on Mars.

In order for that to work, you have to land a 3D printing machine on Mars along with the raw materials. Can it be done? Sure. Do you want to rely on the 3D printer and a skilled operator or spare pre-manufactured parts shipped? In any event, I think inflatable or expandable heat shields like HIAD and ADEPT are the best ways to keep reentry mass down.

SpaceNut wrote:

We have had other advances ain 3D printing capability and will also post thos there instead to keep the topic going on the Smallest Human Ascent or Descent Lander for Mars or Earth.

No doubt 3D printing is starting to come into its own. It's a really impressive technology, but I think shipping every cargo container to Mars with ADEPT is a better option.

SpaceNut wrote:

Based on numbers for the 2 destinations we have deverging designs and applications from the base plans as we have differing conditions for when the astronaut lands to contend with.

I'm not sure what you're making reference to.

SpaceNut wrote:

On Earth an astronaut is able to walk away from the landing site and go for any place within walking distance but on Mars the limitation is the space suits life support and the physical condition of the astronaut as you can only go as long as the space suit is working.....

That's true, but the space suit has to be a very high reliability device to even entertain a surface exploration campaign. The reason the idea of walking a kilometer or two to a habitat seems like a bad idea is that current space suit designs are unsuitable for use in planetary environments. Personally, I think an astronaut should be able to walk 5 km in a MCP suit to even be considered for a Mars mission.

GW Johnson · 2016-01-08 11:12:30

To answer kbd512's questions about Gemini-B/MOL, I went looking on the internet. I had the date wrong, the test flight was 1966, program was cancelled in 1969 in favor of unmanned spy satellites.

The capsule was the unmanned Gemini-2 test flight capsule refurbished with a new larger-diameter heatshield (complete with hatch) to represent a prototype for the revised Gemini-B configuration. That capsule is on display in a USAF museum at Cape Canaveral, along with a mockup of the real Gemini-B design.

The real Gemini-B capsule designs had considerable interior changes to layout to make way for astronauts to use that hatch to enter MOL. The larger heat shield diameter was an upgrade to handle slightly-higher entry energies from polar orbit. The test flight used the prototype capsule and a mostly-mass model dummy for the MOL space station. It was launched with a Titan-IIIC. Purpose of the test was to demonstrate adequacy of the new heat shield with the hatch through it, and they did.

MOL was not a NASA program, it was a USAF program. The military would do things NASA would not do, even then, such as simply refurbish and re-fly a capsule. That situation is even more disparate today.

MOL was a manned spy satellite intended for a 40-day mission. It was cancelled in favor of the KH-10/-11 unmanned spy satellite series. The Russians flew their equivalent, Almaz, on 3 manned missions, before cancelling it in favor of their unmanned satellite program, just as we did.

GW

SpaceNut · 2016-01-09 10:12:51

The first item up in the design of the unpressurized landing vehicle is life support and with current time projects that is about 8 hours with what a man can carry......Next up is the condition of the astronauts ability to be mobile after the journey out to mars....Then lastly the distance to travas from point a landing site of the habitat or other vehicle with life support and to where the small lander arrives at such that the distance is even possible to get to the habitat as the topographymay be to ruggard for the crew man to climb or hike through. Which brings me to success or failure via these key points.

from other topic edit:
Link page 26 indicates hydrogen fuel and continues the choice selection of fuels on page 45 forward.
The link is no sky crane and that belongs in the other topic.

I do agree that we need to make things as lite as possible but not at the sacrifice of crew or mission.
Is there a place for both vehicle types, I do believe so but at what stage of mission are we to introduce each is the question.

The disposable methods of nasa's use once especially for mars landings does cost as indicated it takes a factor of nearly 20 times that to which we deliver to mars versus what we need to push it into orbit. Now that is costly....

So yes we do need a minimalist landing capability ( in smallest landing ascent vehicle) and also one that is larger for other purposes. So be it that if we do want a small lander lets talk about that in that topic....

GW Johnson · 2016-01-09 10:43:33

OK, there are two completely different approaches to landing men on Mars. The selection between them depends upon what you have ready to use at the time you freeze the design and start building hardware. Whichever way you go, you simply have to belly-up to the bar and pay the bill. If you really want to go.

Trying to be too cheap is how we ended up with an oversize, semi-unsafe shuttle design which was anything but the cheap/reusable craft that it was supposed to be. There's a lot more to this than just the price tag, as important as that is.

If you choose to land multiple vehicles at the same site (which has huge advantages in reducing thrown masses and diameters), then you absolutely will have to solve the landing accuracy problem. Because if you don't, and your manned vehicle misses the mark by, say, 300 km (something that first happened on Scott Carpenter's Mercury flight, and multiple times since), your crew will die if their lander is not 2-way and already fueled for the ascent. That's not the sort of thing a surface rover can make make up for.

Also incurred if you choose to land multiple vehicles at the same site is a site restriction to generally smooth terrain. That is to enable astronauts to walk or drive a rover a few km to the other vehicles where the supplies are. Plus, you need to take with you a few satellites to leave in Mars orbit to start-up a GPS system You have to do this in order to achieve 1 km accuracy. That very definitely means some of your stuff has to go to Mars orbit and not direct to the surface. It's not just something of trivial size that you drop off on the way down, as the velocities don't match.

All of that "goes away" of you choose to go down in one big landing boat. But, you have throw much larger masses and diameters to Mars, and you end up basing in LMO for at least the first half of your stay there.

The issue of astronaut fitness to land and to walk distances simply requires artificial gravity at something near 1 gee during the trip to Mars. No other way is known to guarantee that on 6-to-9 month time scales, and NASA is 20 years (at least) delinquent in facing up to that fact. So are a lot of other folks. This applies to both approaches, period.

The same applies to the voyage home. If you choose to do a free return in a small capsule (throwing away a lot of expensive spaceship, which I think is stupid) the entry is about 50,000 ft/sec (15 km/s) and will run 12-15 gee peak. You must be fully healthy to survive that. Period. Even if you choose to return to LEO and do a 3-4 gee capsule entry from there, your emergency bailout is still the free return. So the 1-gee health situation is a requirement that is absolute, for either approach.

GW

ps -- and I still think exploring multiple sites makes more sense, which leans toward the landing boat idea for practicality. How do you visit a site 1000-2000 km away with a rover whose range might be 100-300 km unrefueled, and with completely unexplored, probably rather-rough terrain in between? There is the lesson of Curiosity's aluminum "tires" to consider.

Last edited by GW Johnson (2016-01-09 10:54:55)

kbd512 · 2016-01-09 15:00:35

GW Johnson wrote:

OK, there are two completely different approaches to landing men on Mars. The selection between them depends upon what you have ready to use at the time you freeze the design and start building hardware. Whichever way you go, you simply have to belly-up to the bar and pay the bill. If you really want to go.

You have to have money in your pocket to buy things from the bar (private sector). You can't go to the bar with money you don't have. The unpressurized minimalist capsule design, whether for a single person or four people, is about funding reality. We can afford the unpressurized capsule. We can't afford the pressurized all-in-one MDV/MAV/habitation solution. Admit to reality and then start hardware development.

GW Johnson wrote:

Trying to be too cheap is how we ended up with an oversize, semi-unsafe shuttle design which was anything but the cheap/reusable craft that it was supposed to be. There's a lot more to this than just the price tag, as important as that is.

I think that first statement is inaccurate. The Space Shuttle's design was compromised by conflicting requirements. That's exactly what I'm trying to avoid here.

With respect to the second statement, I think money is pretty much all there is to it. Money is always a major factor in every government program.

My MDV design is a single purpose solution. It's your ride to the surface and that's it.

My MAV design is a single purpose solution. It's your ride back to the MTV and that's it.

Both designs can use the same astronaut container, but both have different support hardware requirements. Instead of allowing engineers to prove how clever they can be, admit that the design requirements are different and go forward with separate solutions for each.

GW Johnson wrote:

If you choose to land multiple vehicles at the same site (which has huge advantages in reducing thrown masses and diameters), then you absolutely will have to solve the landing accuracy problem. Because if you don't, and your manned vehicle misses the mark by, say, 300 km (something that first happened on Scott Carpenter's Mercury flight, and multiple times since), your crew will die if their lander is not 2-way and already fueled for the ascent. That's not the sort of thing a surface rover can make make up for.

If your surface exploration solution is mobile, landing a few kilometers off course is not a major problem. The rovers can reach you in less than an hour. If you can't land reliably land within 25km of your target, then don't land until your accuracy improves.

GW Johnson wrote:

Also incurred if you choose to land multiple vehicles at the same site is a site restriction to generally smooth terrain. That is to enable astronauts to walk or drive a rover a few km to the other vehicles where the supplies are. Plus, you need to take with you a few satellites to leave in Mars orbit to start-up a GPS system You have to do this in order to achieve 1 km accuracy. That very definitely means some of your stuff has to go to Mars orbit and not direct to the surface. It's not just something of trivial size that you drop off on the way down, as the velocities don't match.

If the vehicles are tracked pressurized rovers, then the terrain is not likely to be a major problem. If ringing the planet with GPS satellites is required for precision landing, then that's what we have to do.

GW Johnson wrote:

All of that "goes away" of you choose to go down in one big landing boat. But, you have throw much larger masses and diameters to Mars, and you end up basing in LMO for at least the first half of your stay there.

We should land the astronauts in a habitat module if the landing precision problem is that much of a problem. As you stated, we're only able to use the "big lander" solution with rockets we don't have developed with funding NASA isn't going to get. I think landing precision isn't that much of a problem, although clearly it's a design consideration. Viking didn't land 300km off target.

GW Johnson wrote:

The issue of astronaut fitness to land and to walk distances simply requires artificial gravity at something near 1 gee during the trip to Mars. No other way is known to guarantee that on 6-to-9 month time scales, and NASA is 20 years (at least) delinquent in facing up to that fact. So are a lot of other folks. This applies to both approaches, period.

Artificial gravity should be a fundamental design feature of any interplanetary spacecraft intended to transport humans. The fact that it's absent from all of NASA's deep space habitat designs is more evidence that they're more concerned with giving contractors something to do than designing hardware that accounts for human physiology.

GW Johnson wrote:

The same applies to the voyage home. If you choose to do a free return in a small capsule (throwing away a lot of expensive spaceship, which I think is stupid) the entry is about 50,000 ft/sec (15 km/s) and will run 12-15 gee peak. You must be fully healthy to survive that. Period. Even if you choose to return to LEO and do a 3-4 gee capsule entry from there, your emergency bailout is still the free return. So the 1-gee health situation is a requirement that is absolute, for either approach.

Agreed.

GW Johnson wrote:

GW

GW Johnson wrote:

ps -- and I still think exploring multiple sites makes more sense, which leans toward the landing boat idea for practicality. How do you visit a site 1000-2000 km away with a rover whose range might be 100-300 km unrefueled, and with completely unexplored, probably rather-rough terrain in between? There is the lesson of Curiosity's aluminum "tires" to consider.

I think the best way to explore multiple sites is to mount multiple missions and use multiple pressurized nuclear powered rovers that aren't artificially limited by sunlight or hydrocarbon fuels. It's a lot less expensive to ship spare rover parts and support equipment for the rovers than it is to design reusable rockets refueled on Mars. I could be wrong about that, but here on Earth M113 repair is a lot less involved than Space Shuttle repair, incomparably less expensive, and generally done in field conditions without a lot of support equipment.

You never know exactly what you're going to find or where you're going to find it, and that is what makes tracked nuclear powered rovers so attractive for Mars exploration.

SpaceNut · 2016-01-10 19:56:45

We need tracking beacons landed in the landing site arena that we want to be put down in for being able to time the craft down to the surface more acurately.....These can be solar powered along the equator....these are small stationary landers. They do not need to be exact in placement or distance just active once in place....We can also monitor the strobing signal on the way down once the heatshield are dumped and parachutes are open and with a few more pieces we can make the chute steerable....once engines begin firing then we can even use it to better control the pitch angle and final approach to the landing site....

kbd512 · 2016-01-10 21:11:57

SpaceNut wrote:

We need tracking beacons landed in the landing site arena that we want to be put down in for being able to time the craft down to the surface more acurately.....These can be solar powered along the equator....these are small stationary landers. They do not need to be exact in placement or distance just active once in place....We can also monitor the strobing signal on the way down once the heatshield are dumped and parachutes are open and with a few more pieces we can make the chute steerable....once engines begin firing then we can even use it to better control the pitch angle and final approach to the landing site....

Landing beacons are the absolute best way to assure hitting your target. If reentry goes smoothly and you have a steerable parachute, then you can hit your target with a fair degree of precision. If you have pressurized rovers ring the landing area, then if you can simply land in the correct general area there will be a rover waiting for you in under an hour. There's little need for so much fuss over operations that have been executed successfully so many times before.

I feel like I'm beating a dead horse here, but if the capsule is light enough and you can force a parachute open of sufficient diameter, then you don't need rockets. That solution is so attractive from a mass, complexity, and cost standpoint that it at least merits trying it. There's nothing desirable about carrying the weight of an active propulsion system to Mars if you can avoid it.

SpaceNut · 2016-01-10 21:54:59

The parachute for MSL /Skycrane useage were problematic in design to get it to open.... as you will see from the image its not a simple canopy as it has a gap in the webbing.
http://www.nasa.gov/centers/ames/resear … chute.html

NASA's Mars Science Laboratory mission opens to a diameter of nearly 16 meters (51 feet).

kbd512 · 2016-01-10 22:26:44

The parachute I want to use is square and has an inflatable collar with stiffeners for control (most likely carbon fiber strips sewn into the fabric). The portion of that MSL parachute that's colored orange would be the inflatable collar. Parts of the central canopy may also need an inflatable collar (like an inflatable "X" that runs from the corners of the square to the center to the center of the canopy). Basically, CO2 cartridges force the canopy open, so you can inflate the canopy of a parachute that's otherwise too large for airflow alone to open.

Terraformer · 2016-01-11 05:46:13

Can we use gliders to land on Mars, as Wernher von Braun proposed to do? Obviously the specific proposal of his wouldn't work, but I'm thinking of something like the FIRST glider. Perhaps having wings which could fold out for reentry, and then be retracted on the surface so it can take off again? Maybe a vertical takeoff and a horizontal landing.

SpaceNut · 2016-01-11 19:42:03

Steerable parachute have a couple of patents that I located while searching for the R&D work...
http://www.google.com/patents/US6889942
http://www.google.com/patents/US3013753
Both have abstracts on what they consider is the patent content and each have a lengthy list of other patents to reference at there documents end.

Now for the science of what is a steerable parachute.
First up is in the glider shape family
Beamer 3 Reserve Parachute by High Adventure ~ Steerable

Automatic steerable parachute used for the first time on a wildfire

Dynamic Parachute Control System - Shawn Liang and Marc Udoff

Joint Precision Airdrop System (JPADS)

SpaceNut · 2016-08-30 17:47:07

Bump seems appropiate for a tonne at a time to be delivered to the mars surface.

elderflower · 2016-08-31 04:27:35

I would think about a multi use device. A rocket powered hopper for use as local transport. Add a second stage (disposable or reuseable) to get into orbit and rendezvous with a larger ship for earth return. Leave the hopper in Mars orbit for use by the next group.

Terraformer · 2016-08-31 07:23:10

With landing beacons, how close can we land payloads to our site? Having supplies dotted around a kilometre wide circle isn't that much of a problem if you have a rover to pick them up.

elderflower · 2016-08-31 08:42:11

First find a good landing area, then place a beacon. Check position of beacon is good, then land the first load, with another beacon, near it. You could have, say eight loads landed in a circle around the first beacon, each in its own sector and none landing on top of one another. This only works with power landing, but not Skycranes as you don't want an exhausted one of those landing on your cargo, or your beacon.

Last edited by elderflower (2016-08-31 09:11:11)

SpaceNut · 2016-08-31 19:22:30

The trouble with radio beacons are with frequency where is the blackout located on the descent path as the mars atmospheric density is quite variable and with entry speed as well.

Radio Wave Propagation Handbook for Communication on and Around Mars

The Mars Science Laboratory EDL Communications Brownout and Blackout at UHF

The UHF relay links from MSL to the Mars Reconnaissance Orbiter (MRO) and to the Mars Express (MEX) suffered a period of ~70 s of degradation, consisting of a combination of brownout (signal fades) and blackout (complete loss of signal) that coincided with the predicted period of signal degradation from preflight analyses. The observed signal fades and outages on both signal links spanned the interval from ~30 s to ~95 s after entry at the atmospheric interface.

kbd512 · 2016-09-02 16:25:14

I thought of another technique to increase the effective drag produced by a parachute that would not require inflatable collars (concentric parachutes) and, as always, someone else already thought of it:

US Patent 20110290944

Would this work on Mars? I really don't know. Compared to supersonic retro-propulsion systems, parachutes are really easy and comparatively inexpensive to test. If we're going to spend tens to hundreds of millions on the fuel required to deliver EDL fuel to another planet (R&D costs for supersonic retro-propulsion plus hardware required to actually deliver the EDL fuel and propulsion hardware), it's probably a good idea to first determine whether or not that's even necessary before committing funding to a solution in search of a problem.

Nearly any parachute-based solution that can be made to function correctly will be the simplest, lowest mass, least costly, and least dangerous solution to the problem of transporting humans to the surface of Mars. If it's possible to steer the parachute, that's just icing on the cake. The real technological victory is passive EDL.

If this solution or something like it scales to 5t, then there's very little incentive to pursuing more complicated EDL solutions for mere surface exploration. More complicated active EDL solutions are likely to require another decade of testing and refinement. Passive EDL should be a two year problem to solution or determine is completely infeasible.

There's not enough funding available for development and testing of active EDL right now, so let's either prove out or rule out passive EDL with the small amounts of funding that are available.

GW Johnson · 2016-09-04 11:23:49

I don't question that parachute systems, if they can be made to work correctly on Mars, will be the lightest and least expensive option. That has long been well-known. But, the history of ever-heavier probes sent to Mars says the limit there is about a ton or so delivered to the surface, even in the denser "air" in the lowlands, and even that requires a last-second retro thrust to reduce speeds and impact forces to survivable values. (Air bags as an alternative to last-second retro thrust only work well in smaller sizes.)

Chutes and other aero-decelerators have a mass-dependent scaling limit in air that thin (0.6% the pressure here, varying strongly with local elevations from density ratio (to Earth standard) 0.01-ish in the lowlands to very near vacuum in the highlands). That's why flight tests with Mars chutes take place here significantly above 100,000 feet. Density ratios up there are under the 0.014 of 100,000 feet. They drop by an order of magnitude between there and 150,000 feet, and another order of magnitude to 200,000 feet.

Retropropulsion is not mass-limited, it just costs more. But it works at any size, and carries even fewer risks the thinner the "air" is. Those risks involve attitude-disturbing forces from supersonic retro plume instability in the atmosphere. However, the retropropulsive booster landings demonstrated so far by Spacex and Blue Origin are showing that risk not to be as great as once feared.

There's even 1960-vintage NASA wind tunnel data with a Mercury capsule shape showing that retro plume presence does reduce object drag a little bit; it's quoted in my copy of Hoerner's drag bible. That's a bad thing in EDL work, but it is quite easily overcome by increasing the retro thrust a tad.

Retropropulsive landings are how Spacex plans to land its manned Dragon right here on Earth, in spite of the long history of US chute ocean landings. The Russian survived land impact with last-second retro thrust or by bailing out before impact, and still do today. But for Spacex's manned Dragon, the chutes are nothing but an emergency backup. And that is a deliberate choice.

The extra weight and costs of the rockets and propellant buy two very important returns for Spacex: (1) much softer touchdowns than anything you can have with chutes, which greatly enhances the reusability of the capsule, and which also makes land landings easily feasible virtually anywhere on the globe, and (2) the super-high landing precision coupled with easy land landing capability (once you fully learn retropropulsive vehicle control), something which far simplifies recovery and thus lowers recovery costs by an enormous amount (no fleet of boats and crews to hire).

Result: net savings. That's why they are doing what seems so counterintuitive until you look closely. Actually it makes very good sense.

GW

Last edited by GW Johnson (2016-09-04 14:59:28)

kbd512 · 2016-09-06 16:43:04

GW,

I hear you. I still want to know if it's possible and the only way to know with certainty is to test the concept. Parachutes costs so little in comparison to supersonic retro-propulsion that I think it's worth a test. If a cargo delivery fails, then it fails. If the cargo required to support human exploration of Mars is not already on the surface and confirmed as in-tact, we wouldn't even attempt the mission. The last requirement before human exploration is always to get the humans there, unharmed. "There is nothing as expensive as a dead crew."

SpaceNut · 2016-09-06 17:25:19

To do the experiment since we must be able to prove retro rocket landing at speed we will need to scale mars number for Earth tests. So 40 Mt on mars surface landing on earth means roughly 120 mt craft for the near orbit reentry and that just a large capsule or habitat can.....

https://en.wikipedia.org/wiki/Mars_atmospheric_entry

NASA is carrying out research on retropropulsive deceleration technologies to develop new approaches to Mars atmospheric entry. A key problem with propulsive techniques is handling the fluid flow problems and attitude control of the descent vehicle during the supersonic retropropulsion phase of the entry and deceleration. More specifically, NASA is carrying out thermal imaging infrared sensor data-gathering studies of the SpaceX booster controlled-descent tests that are currently, as of 2014, underway. The research team is particularly interested in the 70–40-kilometer (43–25 mi) altitude range of the SpaceX "reentry burn" on the Falcon 9 Earth-entry tests as this is the "powered flight through the Mars-relevant retropulsion regime" that models Mars entry and descent conditions.

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#151 2016-01-06 22:02:44

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#152 2016-01-06 23:53:11

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#153 2016-01-07 11:40:02

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#154 2016-01-07 16:39:37

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#155 2016-01-07 20:03:11

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#156 2016-01-07 21:44:35

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#157 2016-01-08 11:12:30

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#158 2016-01-09 10:12:51

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#159 2016-01-09 10:43:33

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#160 2016-01-09 15:00:35

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#161 2016-01-10 19:56:45

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#162 2016-01-10 21:11:57

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#163 2016-01-10 21:54:59

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#164 2016-01-10 22:26:44

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#165 2016-01-11 05:46:13

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#166 2016-01-11 19:42:03

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#167 2016-08-30 17:47:07

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#168 2016-08-31 04:27:35

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#169 2016-08-31 07:23:10

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#170 2016-08-31 08:42:11

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#171 2016-08-31 19:22:30

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#172 2016-09-02 16:25:14

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#173 2016-09-04 11:23:49

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#174 2016-09-06 16:43:04

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

#175 2016-09-06 17:25:19

Re: Smallest Human Ascent or Descent Lander for Mars Or Earth

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