Comparison of landing methods for capsules, boosters or probes

[AngelLestat]

What of these methods is better to land capsules, boosters or probes?

Normal parachutes:

-the technology is very mature, it works.

-descent is not guided

-terminal speed still high

-considerable mass added

-required high space volume

-it needs heat protection.

-regular with turbulance, bad with high winds.

Wing shape parachutes:

-the technology is very mature but not in current use for the named examples.

-descent is guided

-required mass and space a bit lower than normal parachutes.

-softer descent than normal parachutes

-it needs heat protection

-bad with turbulance, regular with high winds.

-it can not be partially open so easily as normal parachutes, so the acceleration force is stronger.

Heli-blades

http://www.nasa.gov/centers/kennedy/news/rotocapsule.html

"the wind passing over the rotors as the capsule descends would make the blades turn, a process called auto-rotation that has been proven repeatedly on helicopters but never tried on spacecraft"

Close to the ground you can vary the blades angle to convert high rotation speed energy into extra drag which it gives a softer landing without big blades.

A similar concept is used by the maple seed:

-part of the technology is very mature, we need to learn the best way to integrate to current capsules, probes or boosters.

-descent is guided

-very soft landing

-Less mass than parachutes

-less volume than parachutes

-it may avoid heat protections in some cases.

-regular with turbulance, regular with high winds.

Rocket thruster

-the technology is mature but not highly tested, spacex choice.

-descent is guided, extra fuel provide a big change in landing location.

-required mass and space depends how much we want to change our landing location, for just landing may be similar or a bit higher than parachutes.

-it can land in planets without atmospheres.

-a thruster may be welcome in any kind of spacecraft to be used for different purposes.

-it does not need much heat protection.

-very soft landing.

-bad or good with turbulance and high winds depending if it is a booster or capsule.

-ignition and thruster mechanism are complex, so they may fail.

Wings or lifting body shape:

-the technology is very mature, but aerodynamics are complex, so it requires hard developing and testing.

-descent is guided, it can achieve long distances. It needs a landing strip.

-mass and volume needed is less than normal parachutes, it can be used to lower reentry speeds.

-soft landing

-regular (close to good) with turbulance and high wind speeds.

-they may be a problem in rocket ascent or to be included inside farings.

Lithobraking:

Used more frequently as a complementary method to landing but although with high potential in some particular cases as main method. Breakthrough in materials will increase by a lot its performance.

-common used for short deltav changes or high depending surface density and payload hardness.

-very low volume and mass required.

-hard landing

-descent is not guided.

-good with turbulance and high wind speeds.

-heat is not a real issue.

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Some of those pross and cons depends on my opinion and knowledge, so they may be wrong.

I am not sure if I include all possible methods.

In your opinion, which method should be used for each case? it will need a backup method, which one?

Edited August 27, 2015 by AngelLestat
Lithobraking added (k2 request)

[Bill Phil]

Probably the parachute. It's pretty easy to do... Unless you're on Mars...

[Kertherina]

For me active (thruster) landing for capsules, without question.

- Rocket technology is mature as you said, you can add redundancy for extra security like SpaceX does.

- It doesn't need much mass

- Abort capability straight up to orbit

- Soft pinpoint landings

- Edit: and launch abort system is also included!

It's just a combination of security and versatility, plus it allows reusability (no landings in salt water) and even rapid reusability, that makes it superior in my opinion. A backup parachute for redundancy doesn't hurt either, giving you two very different landing options (different again means more secure because not everything that destroys a chute destroys engines and vice versa) for earth at least. I can't wait until the first Dragon V2s land actively, i think it is the future.

EDIT: For boosters, since you already have an engine why not reuse it? Additional parachutes or something else would add way more dead weight than a bit extra fuel, see SpaceX again.

For probes, parachutes can be super handy, but that obviously depends on the target. On a planet with atmosphere you should use it, without atmosphere you have no other option than active landing, and on Mars you could in theory to both (only parachute is not an option), but then pure active landing might just be the way to go because it is simpler than having two different systems to land.

Edited March 14, 2015 by Kertherina

[Bill Phil]

For me active (thruster) landing, without question.

- Rocket technology is mature as you said, you can add redundancy for extra security like SpaceX does.

- It doesn't need much mass

- Abort capability straight up to orbit

- Soft pinpoint landings

It's just a combination of security and versatility, plus it allows reusability (no landings in salt water) and even rapid reusability, that makes it superior in my opinion. A backup parachute for redundancy doesn't hurt either, giving you two very different landing options (different again means more secure because not everything that destroys a chute destroys engines and vice versa) for earth at least. I can't wait until the first Dragon V2s land actively, i think it is the future.

Thrusters are very heavy, need fuel, and can't abort to orbit.

Now, if you go Soviet-style and use parachutes and small solid thrusters to slow down near the ground, you get a ground landing.

[Kertherina]

Thrusters are very heavy, need fuel, and can't abort to orbit.

You again save the weight of a launch escape system though, which is really heavy. Also, generally the weight of parachutes is underestimated. I don't remember any numbers, but i read that thrusters are in fact lighter than parachutes for a Dragon like capsule.

[Bill Phil]

You again save the weight of a launch escape system though, which is really heavy. Also, generally the weight of parachutes is underestimated. I don't remember any numbers, but i read that thrusters are in fact lighter than parachutes for a Dragon like capsule.

The mass of Dragon is a few tons. Thrusters require propellant, space, and the thruster itself. The weight adds up. They're probably quite close in mass...

Parachutes are much simpler, and Launch Abort Systems can be made to be lighter.

Plus, source?

[Kibble]

Parachutes.

[AngelLestat]

I add the wing case which I forget, also some pictures :S

When someone said parachutes, please define if is normal parachutes or wing shape parachutes.

In my opinion, normal parachutes is the worst method, of course is very well tested and it works fine to land in sea (it needs rocket thrusters to land on ground)

The thing why they never were remplaced, was just because the space industry is allergic to changes.

If somebody in charge of a mission or development said "lets test with another landing method", he/she risk to lose his/her job in case something wrong happen, but if something wrong happen with parachutes, then is not his/her responsibility.

But I guess space industry should be in the edge of technology, not in the bottom.

Take into account that you can choose combinations, for example rocket thrusters with heli-blades, etc.

I guess parachutes and rocket thrusters are more risky than the heli-blade or wing method, so is more probably they need backup methods.

Edited March 14, 2015 by AngelLestat

[Bill Phil]

I add the wing case which I forget, also some pictures :S

When someone said parachutes, please define if is normal parachutes or wing shape parachutes.

In my opinion, normal parachutes is the worst method, of course is very well tested and it works fine to land in sea (it needs rocket thrusters to land on ground)

The thing why they never were remplaced, was just because the space industry is allergic to changes.

If somebody in charge of a mission or development said "lets test with another landing method", he/she risk to lose his/her job in case something wrong happen, but if something wrong happen with parachutes, then is not his/her responsibility.

But I guess space industry should be in the edge of technology, not in the bottom.

Take into account that you can choose combinations, for example rocket thrusters with heli-blades, etc.

I guess parachutes and rocket thrusters are more risky than the heli-blade or wing method, so is more probably they need backup methods.

Soyuz can land on ground, in fact it's supposed to land on ground and routinely does.

Using small solid thrusters to brake at the last moment would allow you to land on land. And the Russians have done it for decades with few complications.

Rockets are complicated. Parachutes and solid rockets are not as complicated. It's complication that counts. A more advanced system would have more parts and thus more chances to mess up.

[magnemoe]

The mass of Dragon is a few tons. Thrusters require propellant, space, and the thruster itself. The weight adds up. They're probably quite close in mass...

Parachutes are much simpler, and Launch Abort Systems can be made to be lighter.

Plus, source?

Dragon includes the service module who is dropped before reentry for other pods so launching an dragon is not significantly heavier than other pods with their service module.

The trusters has some benefits in that they are flexible, if you have to do an escape second after launch they can either do an redirect to an sea landing or conserve some fuel for an braking burn at touchdown on ground.

One interesting idea might be to combine an lifting body like dreamchaser with an parasail, this has the benefit that you can land with horizontal speed on a runway.

Main problem with the parasail is that its an single failure point, you tend to use multiple parachutes,

[Bill Phil]

Dragon includes the service module who is dropped before reentry for other pods so launching an dragon is not significantly heavier than other pods with their service module.

The trusters has some benefits in that they are flexible, if you have to do an escape second after launch they can either do an redirect to an sea landing or conserve some fuel for an braking burn at touchdown on ground.

One interesting idea might be to combine an lifting body like dreamchaser with an parasail, this has the benefit that you can land with horizontal speed on a runway.

Main problem with the parasail is that its an single failure point, you tend to use multiple parachutes,

You could easily just use an LES. And having parachutes as a back-up in case of engine failure on decent is a good idea. That and solids like Soyuz.

[Armchair Rocket Scientist]

Dragon includes the service module who is dropped before reentry for other pods so launching an dragon is not significantly heavier than other pods with their service module.

Actually, Dragon's trunk is probably a lot lighter than most service modules: in most manned spacecraft, most of the propellant, thrusters, and some life support equipment is in the service module, while in Dragon these components are all in the back of the capsule, and the trunk only contains solar panels, radiators, and some space for unpressurized payloads.

[HoloYolo]

For me, Parachutes of any kind. Here is why.

1. Not very heavy compared to rockets (of course they can't be used on Mars or bodies with no atmosphere)

2. Cheaper in the long run

3 Safer. What if the rockets fail and they don't have parachutes? The contents of said vessel would be killed and/or destroyed

4 Can be used in basically any weather.

[Superluminaut]

In short, rocket thrust for pinpoint landings and parachutes if landing location is irrelevant.

So basically manned space crafts, probes for specific locations, booster returns, cargo supply/return, etc should use a powered descent. Imagine if your commercial jets used a parachute landing every time cause its "safer".

Most everything else is probably cost constrained and a parachute would be simpler, unless the object gets picked up by a powered descent capable spacecraft.

I imagine some unique situation exist, like a very small rocket in which wings make sense, or a bad weather probe could use heli blades, or spyspaceplanes.

[Bill Phil]

So basically manned space crafts, probes for specific locations, booster returns, cargo supply/return, etc should use a powered descent. Imagine if your commercial jets used a parachute landing every time cause its "safer".

This comparison is not valid. Aircraft don't have thrusters to provide force against gravity. They rely on lift. Lift is dependent on speed and wing shape. It's not dependent on onboard fuel. Well... the speed part is. But it's much more efficient because the airspeed adds to the exhaust velocity.

[Superluminaut]

Launch Abort Systems can be made to be lighter.

Can they really? I thought the typical tower launch escape system requires ballast proportional to the weight of whatever it lifts away.

- - - Updated - - -

This comparison is not valid. Aircraft don't have thrusters to provide force against gravity. They rely on lift. Lift is dependent on speed and wing shape. It's not dependent on onboard fuel. Well... the speed part is. But it's much more efficient because the airspeed adds to the exhaust velocity.

My point was more along the lines of lift having once been novel, yet we still land with it.

- - - Updated - - -

Also one point on powered descent failures, you can use redundant thrusters. The dragon V2 for instance uses 8 thrusters, and I am assuming this but I would expect it could perform and emergency landing on just 2.

[Bill Phil]

Can they really? I thought the typical tower launch escape system requires ballast proportional to the weight of whatever it lifts away.

- - - Updated - - -

My point was more along the lines of lift having once been novel, yet we still land with it.

Towers can be lightened by using new materials, and using smarter comstruction (Mecury style, with holes in it, it barely affected the performance).

Lift was once novel, but it in no way is comparable to a thruster for a powered landing. Aircraft =/= spacecraft.

- - - Updated - - -

Also one point on powered descent failures, you can use redundant thrusters. The dragon V2 for instance uses 8 thrusters, and I am assuming this but I would expect it could perform and emergency landing on just 2.

Superdracos? Sure. But those are heavy, i bet.

[Airlock]

Having thrusters available for fully propulsive landings (Dragon 2) and propulsive assist (Soyuz) offers a greater assortment of tangential abilities during a mission. While fully propulsive landings will become the norm for the Crew Dragon in the long run, SpaceX needs to complete a certification process over the next few years before they can do it with crew aboard. The first flights will be standard parachute splashdowns. Then they'll transition to propulsive-assisted parachute landings on land, before finally moving to fully-propulsive further down the road. The Dragonfly vehicle will demonstrate various propulsive modes at the McGregor test facility as well.

If anything, this certification process displays how much redundancy the Dragon 2 has built into it. With a maneuvering and escape system in the capsule's sidewall, the same hypergolics are shared for launch-abort, on-orbit maneuvers, and landing. The crew is also provided the ability to abort at any point throughout a flight. (pad abort, ascent abort, abort to orbit, parachute splashdown in event of engine failure, etc).

Here's a slightly-dated video showing a Dragon 2 concept doing a propulsive-assisted parachute landing in the desert, similar to Soyuz.

And here's a recent statement on crew operations made by SpaceX before a Congressional hearing on Commercial Crew.

http://science.house.gov/sites/republicans.science.house.gov/files/documents/HHRG-114-SY16-WState-GReisman-20150227.pdf

The relevant part:

The crew Dragon’s SuperDraco engines are divided into four quads, each with two SuperDracos and 4 Draco engines. The SuperDracos will activate to provide precision land landing capability. Nominally, only two quads are used for on-orbit propellant with the Dracos and two quads are reserved for propulsive landing using the SuperDracos. For aborts or on-orbit faults, all four quads are available for Draco or SuperDraco operations, increasing flexibility, robustness, and performance in thesecritical situations.

Edited March 15, 2015 by Airlock

[Vanamonde]

How "guided" are autorotating blade arrangements? Isn't that more of a retarded fall?

[shynung]

How "guided" are autorotating blade arrangements? Isn't that more of a retarded fall?

Like a helicopter. As in, the blades' individual angles-of-attack can be varied in reference to its position relative to the craft, i.e. blades on the ventral side had their AoA decreased, the craft veers into that direction, etc. Modern helicopters used a swashplate mechanism to do this.

Anyway, I found an old discussion related to this matter.

Edited March 15, 2015 by shynung

[AngelLestat]

I dont know if call it "arragements".

All helicopters can do that.

Even if they have not motor, controls still works.

of course images would explain better than me:

Just using the rotor inclination, an helicopter can reach 300km/h (not thrusters)

So without engine 200 km/h (horizontal) can be achieve it.

Before touch the ground the blades change the pitch angle and the inclination to get a soft landing.

Some real helicopters doing autorotation landing, this is something that everybody should learn if they want their license.

https://youtu.be/E2a9H8Xw8Mo?t=1m47s

https://youtu.be/2voCedPQMUo?t=3m

Edited March 15, 2015 by AngelLestat

[K^2]

How "guided" are autorotating blade arrangements? Isn't that more of a retarded fall?

Typical auto-rotation "glide ratios" are 3:1 to 4:1. So not quite as well as a glider, but way more than you'd expect.

Lithobraking isn't on the list? Shame.

[Nibb31]

What of these methods is better to land capsules, boosters or probes?

It Dependsâ„¢

[Frozen_Heart]

In theory I'd choose the rocket thruster. However it needs more development before I'd pick it over parachutes.

Maybe once spacex has proven it I'll fully trust that method.

[RainDreamer]

I prefer lifting body design, because it is the most passive method, which involve basically no moving/active part, which reduce the chance of it failing.

Parachute can be ripped/burned up/fail to open.

Heli-wings are pretty nice and would be my secondary choice, if not for it being almost impossible for manual control due to the pod spinning along with the astronaut in it - it will be very disorientating. And if there are mechanisms to allow it to spin without taking the whole pod to a spin, then those mechanism may fail to spin.

Rocket thruster can have fuel tank leaks/fail to ignite/ignition out of sync

Lifting body? Well, the only way it would fail is if it reenter the wrong way (heatshield side up, for example) or there is a damage in the hull, which means it is better not going down in the first place.

That said, is there anything other than cost and design that stop us from using a few methods together? And shouldn't we try to use more than one in the first place, in case one fail?