Is it there a way for orbital reentry without burning?

[Nothke]

Is there a good way to reentry without atmospheric drag heating? Something like a "shuttlecock" reentry for Space Ship One but for orbital speeds? Or would it be possible to slow down spacecraft before the actuall high drag from atmosphere, but perhaps without propulsion? Of course with considered todays technology and economical capabilities...

Could there be a future in thinking about it? And could it be possible to be more economically and safety acceptable?

 

[DarkenedOne]

Is there a good way to reentry without atmospheric drag heating? Something like a "shuttlecock" reentry for Space Ship One but for orbital speeds? Or would it be possible to slow down spacecraft before the actuall high drag from atmosphere, but perhaps without propulsion? Of course with considered todays technology and economical capabilities...

Could there be a future in thinking about it? And could it be possible to be more economically and safety acceptable?

In order to land on earth one must match speeds with the ground. Coming from orbital velocity, which is around 7km/s, that is a great deal of energy.

One could use thrusters to achieve this, however that would be very expensive. Instead they use aerobrakeing. While risker it is a hell of a lot less expensive only consuming part of the heat shield in the process. It is really the space equivalent for the brakes in a car. They turn the kenetic energy into heat, which is were all of the fire comes from.

Sure there are other ways of doing it, but I think it is the definitely the least expensive one.

 

[aaron38]

This is one of the benefits of any SSTO design. Because an SSTO is mostly a flying fuel tank, on reentry it's an empty flying tank. This gives the craft a much larger surface area / volume to weight ratio than the Shuttle. An Ad Astra issue I had back in college had a graph showing the reentry profiles for both the Shuttle and Venture Star. Venture Star was predicted to see much less heating, and have a more gradual decent than the Shuttle, which drops like a brick.

Reading up on the Skylon proposal, that design is also expected to see half the heating of the Shuttle, and like Venture Star, to be able to use a much more rugged TPS.

So no, aerobraking is always going to be part of the mission profile, because it's (nearly) free delta-v. But if we ever get an SSTO flying, there'll be much less burning than there is now.

 

[Gravity_Ray]

Is there a good way to reentry without atmospheric drag heating? Something like a "shuttlecock" reentry for Space Ship One but for orbital speeds? Or would it be possible to slow down spacecraft before the actuall high drag from atmosphere, but perhaps without propulsion? Of course with considered todays technology and economical capabilities...

Could there be a future in thinking about it? And could it be possible to be more economically and safety acceptable?

Your question is answered by the previous comments, but I think you are confusing a couple of different things.

If you are coming back to Earth from say the Moon. You will need to get some speed to escape the Moon's gravity, AND, you may want to add even more speed to 'speed' up your return to Earth. These velocities are a good thing because you do want to get back before you get old, but they become a bad thing once you reach your destination. Now that you are back to Earth you will want to reduce your velocity (in effect reach zero miles an hour like the previous poster said) so you will have to slow down.

You cannot use the Space Ship one “shuttlecock” configuration for this slowing down because there is no atmosphere in space. So like the other poster said you will have to either use rockets to slow down (and as the poster said this is very expensive in fuel), or aero-brake which uses a heat shield (this part answers your question about slowing down without propulsion).

The “shuttlecock” configuration is used only (in) the atmosphere; remember Space Ship One only “just” got into space, so it really didn’t have any serious speed to get rid of. Then it was able to “float” back to Earth. At the speeds you are returning to Earth with, once you hit the atmosphere you will burn up like a shooting star “shuttlecock” configuration or not.

The “shuttlecock” configuration is for sub-orbital speeds, not orbital speeds. Now I assumed a few things about what you said, so if I misunderstood what you said, sorry, just ignore my post.

I had a post once about using a mélange of re-entry processes’ to get to and from Earth. What I was thinking, was; you come back from the Moon in a space ship that doesn’t slow down (it’s just going between the Earth and the Moon). You are met as it makes its close approach to the Earth by a smaller ‘bus type ship’ and passengers are moved to the smaller ship. That ship flies back to a geosynchronous orbit space station and docks. Then you take the space elevator from that station to sub-orbital distance from Earth (much easier to make a space elevator without it being in the atmosphere all the way down to the ground), jump into your “shuttlecock” type spaceship one and float back to Earth. When you want to leave the Earth you fly to sub-orbital altitude in your spaceship one and dock with the bottom of the elevator and reverse the process. But nobody thought it was going to have any cost savings, but I am a dreamer.

 

[access]

Another issue with your idea Ray is that suborbital is not an altitude it is a speed and as such the space elevator-earth connection is flawed. There is a reason spaceship one will never dock with anything.

Things don't orbit because they're a long way from earth but because they are fast enough to be in continuous free fall

 

[SpaceForAReason]

A DCX style craft would do nicely at this sice it posesses the ability to hover. Timed properly, the ship would just reach apex as it hooks on to the end of the elevator. ...Also not unlike the airplanes that hooked up with the Macon airship (look it up, a very interesting read).

 

[aphh]

One thing to note is that the heatshield provides lift for the vehicle in the athmosphere. Without this lift, the angle of attack would get too steep. Gravity would pull you down much harder, so without thrust to slow you down you would actually gain vertical velocity making things worse.

 

[bdewoody]

This is one of the benefits of any SSTO design. Because an SSTO is mostly a flying fuel tank, on reentry it's an empty flying tank. This gives the craft a much larger surface area / volume to weight ratio than the Shuttle. An Ad Astra issue I had back in college had a graph showing the reentry profiles for both the Shuttle and Venture Star. Venture Star was predicted to see much less heating, and have a more gradual decent than the Shuttle, which drops like a brick.

Reading up on the Skylon proposal, that design is also expected to see half the heating of the Shuttle, and like Venture Star, to be able to use a much more rugged TPS.

So no, aerobraking is always going to be part of the mission profile, because it's (nearly) free delta-v. But if we ever get an SSTO flying, there'll be much less burning than there is now.

That larger surface that would help slow you down on re-entry with less heat would also cause more drag on the way up therefore requiring bigger engines and more fuel.

 

[EarthlingX]

This is one of the benefits of any SSTO design. Because an SSTO is mostly a flying fuel tank, on reentry it's an empty flying tank. This gives the craft a much larger surface area / volume to weight ratio than the Shuttle. An Ad Astra issue I had back in college had a graph showing the reentry profiles for both the Shuttle and Venture Star. Venture Star was predicted to see much less heating, and have a more gradual decent than the Shuttle, which drops like a brick.

Reading up on the Skylon proposal, that design is also expected to see half the heating of the Shuttle, and like Venture Star, to be able to use a much more rugged TPS.

So no, aerobraking is always going to be part of the mission profile, because it's (nearly) free delta-v. But if we ever get an SSTO flying, there'll be much less burning than there is now.

That larger surface that would help slow you down on re-entry with less heat would also cause more drag on the way up therefore requiring bigger engines and more fuel.

Good point, but perhaps some sort of parachutes ? Inflatable heat shield ? Just high enough, in the less dense atmosphere ?
Big surfaces can help you with Isp under 30 km, but no scramjet yet ..

There will be time when we can do without the aero braking, i just suspect that will not be very soon, maybe just for people going back, with in-orbit refueling, Blue Origin style and i think Russians are working on enhanced powered landing for the next Soyuz generation, for them it's just usual, money ..

Just in case .. :
A question about de-orbiting (Space Science and Astronomy)

 

[ThereIWas2]

If you google the word "ballute" you will find lots of material on inflatable heat shields. Back in the old forum I worked out the math for using one of these to land on Mars. Mars is tricky because the air is so thin - you still need to use some thrusters for the last 100m or so. Earth has a considerably higher entry velocity, but also much thicker atmosphere. I do not know how the tradeoffs work out.

The trick is to lose as much velocity as possible up where the air is thinnest, to reduce heating (KE=mv²). So you want as much aerodynamic lifting as you can get, to stretch out the entry

 

[JeffreyNYA]

Could VASIMR be used to slow a craft down to make re-entry heat no so much of an issue. If the engine is reusable and it uses far less fuel that other options it could bring cost way down. That is however if it would actually work.

 

[ThereIWas2]

Any thruster based deceleration takes as long to decelerate you as it does to accelerate you in the first place. VASIMR is not powerful enough to launch something to orbital speeds so is also not powerful enough to slow you down from those same speeds. (A 100 KW VASIMR gives you about 1 N of thrust, which is about a quarter of a pound.) VASIMR is more suited to changing interplanetary orbits once you are already out of a planetary gravity well, where a gentle sustained push pays off.

 

[rcsplinters]

I think the topic of this thread has been well addressed. However, allow me to drag us off on a bit of a tangent.

I frankly don't believe there is a good appreciation of the energies involved in orbital mechanics, orbit insertion and deorbit impacts on the part of the general public. Most of us which have a keen interest in the subject have a decent graps, though I have to admit, I get lost on some of the finer points as to how you overtake an object but still match speed and orbit, but enough of my shortcomings. Sometimes I wonder if general public had a better understanding of just what is required to climb uphill, the mind numbing speed involved, the incredible energy required and the precision with which all the must be harnessed that we might have a more sympathic public with funding, scheduling and risk assessments that face those in space flight.

We used to talk about such things in high school physics and later college but we had the advantage of moon walking astronaunts plastered on all three channels. Today, I'm not sure that the schools still show such interest in these sorts of "gee whiz" aspects of space flight.

 

[vulture4]

Agree planetary return would require dissipating a lot of energy, but not necessarily all at once. Mars spacecraft often do multipass aerocapture without any heatshield. A large spacecraft returning to earth has more energy to dissipate and would likely require some sort of heat shield, but the more area = less heat equation still holds. For return from LEO it's quite possible to use thin deployable braking surfaces to increase surface area.

 

[ThereIWas2]

The old computer game "SpaceWar" (first implemented on the PDP-1) is an excellent way to learn seat-of-the-pants orbital mechanics.

To rendezvous, you start in an elliptical orbit that is on average slightly lower than your target (say the ISS). Lower means faster (in revolutions per hour), so you will overtake. The trick is to time things so that you and the ISS arrive at the point of congruency at the same time; hence the "launch window". A small application of forward thrust raises the low point of your orbit to match the ISS, so your orbits are now the same. You thrust forward to slow down, which is counterintuitive.

Once you master SpaceWar you move up to "Orbiter", which is a whole lot more realistic, and complicated.

 

[kelvinzero]

Long term I have always liked the idea of an orbital monorail loop as a sort of momentum battery, but that would be very long term, after we have industry and mass drivers on the moon, etc. Its really an idea to file alongside space elevators rather than this thread, which seems to have at least its big toe in the present

 

[EarthlingX]

The old computer game "SpaceWar" (first implemented on the PDP-1) is an excellent way to learn seat-of-the-pants orbital mechanics.

To rendezvous, you start in an elliptical orbit that is on average slightly lower than your target (say the ISS). Lower means faster (in revolutions per hour), so you will overtake. The trick is to time things so that you and the ISS arrive at the point of congruency at the same time; hence the "launch window". A small application of forward thrust raises the low point of your orbit to match the ISS, so your orbits are now the same. You thrust forward to slow down, which is counterintuitive.

Once you master SpaceWar you move up to "Orbiter", which is a whole lot more realistic, and complicated.

You tried it ? I had to go to a flight school first, but have it on a short term plan, will report about it on Virtual space tech (forum) ..

 

[Nothke]

If the spacecraft on route to Earth from Mars is also in the line of sun (goes towards Sun), what about using solar sails for braking before entering atmos.? It could be possible

 

[ThereIWas2]

You tried it ?

I've done a couple versions of SpaceWar (including the PDP-1 version). Also spent a lot of time in Orbiter, ultimately trying to do flights between Jovian moons.

 

[ThereIWas2]

If the spacecraft on route to Earth from Mars is also in the line of sun (goes towards Sun), what about using solar sails for braking before entering atmos.? It could be possible

Solar sails are on the same order of thrust as VASIMR, or less, so the answer would be no.

 

[halman]

We have to maintain a distinction between de-orbiting and falling into a gravity well. To return from orbit means lowering your speed enough to fall into the atmosphere, at just the right angle. Falling into a gravity well means that you are going to accelerate as you get closer to the planet. So the energy involved is much higher. Apollo missions had over 25,000 miles per hour of velocity to shed, so they 'skipped' the capsule off the atmosphere a couple of times to lose as much velocity as possible before actual re-entry.

Returning from orbit using thrusters would require the same amount of propellant as reaching orbit.

We have learned how to protect a vehicle from the heat of re-entry with thermal tiles which do not ablate, or burn off, like the old heat shields did. This is in part because we now know that the spacecraft can be protected from the intense heat by the shock wave that travels in front of it. The air turns into a plasma, and reaches around 12,000 to 17,000 degrees, whereas the tiles only have to withstand about 3,000 degrees. If, of course, your angle of re-entry is correct. Too shallow, and you skip back into space, to fall very steeply the next time. Too steep, and you burn up, no matter if you are in a capsule, lifting body, or anvil.

A lifting body is able to convert the forward speed to lift, because it has a flat bottom. The wings are to give it maneuverability.

 

[Jim_LAX]

Returning from Moon or Mars to Earth requires that you slow down to Earth's orbital velocity. Then you will be captured in LEO and we have much experience returning from LEO.
That slowing down to LEO speed is not practical with chemical rockets because of tremendous fuel cost. Solar sail and VASIMR simply do not have the thrust to do the job in the time alloted, but a nuclear rocket does.
A nuclear rocket uses hydrogen fuel in a much more efficient way than a chemical rocket, which burns hydrogen with oxygen. A nuclear rocket is reusable, since it only needs to have its hydrogen fuel tank refilled. Its nuclear core can be used many times and its specific impulse (thrust) is more than double even the best chemical rockets.
Imagine that the nuclear rocket has been parked at a Lagrange Point, where it was serviced and re-fuled. It would then head out to meet you as your space craft returns from Mars or wherever. The nuc rocket can easilly match your speed an course, then hitch onto you craft. It would then thrust to slow you down to about LEO speed, just as you reach Earth. It would then un-hitch and return to its gas station at the Lagrange Point while you make a leasurely descent into Earth's atmosphere.
This is not to different from a long freight train crossing the plains which is joined by additional engines to make the climb over the Rockies. The extra engines then return to wait for another freight train and to refill their fuel tanks. Toot toot!

 

[Aerospace_Cadet]

There is one way I can think of that would allow you to enter the Earth's atmosphere at a speed that would not require a heat shield despite traveling at an orbital velocity. Instead of slowing down you may need to speed up!

The Earth orbits the Sun at a speed of 30 km/s (108,000 km/h or 67,110 mph). If your speed is slightly over 30 km/s and you have the perfect entry angle, as you swing around the Earth it's gravity will slow you down slightly. If the exit angle is exactly 180 degrees opposite to the orbital path of the Earth after you reach your apogee and begin to swing back towards the Earth the actual speed of your spaceship would still be slightly over 30 km/s but your relative speed in relation to the Earth could be anything you wish... even a hover. Too slow and you'd have a very bad day because you would not have the speed needed to "catch" the Earth in its orbit.

 

[ElmiraViking]

Yes.

As slowly as possible.

 

[vulture4]

There is one way I can think of that would allow you to enter the Earth's atmosphere at a speed that would not require a heat shield despite traveling at an orbital velocity. Instead of slowing down you may need to speed up!

The Earth orbits the Sun at a speed of 30 km/s (108,000 km/h or 67,110 mph). If your speed is slightly over 30 km/s and you have the perfect entry angle, as you swing around the Earth it's gravity will slow you down slightly. If the exit angle is exactly 180 degrees opposite to the orbital path of the Earth after you reach your apogee and begin to swing back towards the Earth the actual speed of your spaceship would still be slightly over 30 km/s but your relative speed in relation to the Earth could be anything you wish... even a hover. Too slow and you'd have a very bad day because you would not have the speed needed to "catch" the Earth in its orbit.

It's not quite so easy. As you swing around the earth its gravity will speed you up as you approach, then you will decelerate as you depart. Your trajectory only really depends on your approach velocity relative to Earth; your velocity relative to the sun isn't relevant. Your departure velocity relative to earth will be the same as your approach velocity, unless you did some atmospheric braking.