De-orbiting from LEO revisited - How to avoid highspeed re-entry

dicktice · 2003-04-04 11:24:11

The current method used to re-enter Earth's atmosphere from low Earth orbit (LEO) is essentially brute-force (energy of motion converted to heat, through incandescent ablation of the returning orbiter's high angle-of-attack aerodynamic stagnation surfaces) resulting in the burning away of a portion of either type of space vehicle.
Nothing can be done to avoid this method of reducing speed in the present Space Shuttle or Soyuz flyback vehicles. Descent engines, which could have avoided the need for ablative speed reduction, were not included in either flyback vehicle configuration for reasons that were perhaps valid when their designs had hurriedly to be frozen for political reasons.
Now is the time to produce second-generation redesigns of these obsolescent spacecraft, utilizing existing 1st-stage launchers, that can be slowed down without burning away their surfaces.
In operation, both second-generation flyback vehicles would possess descent engines. After topping-up their fuel tanks, they would undock the ISS, steer a West heading, perform the standard retrograde burn to slow down, then face East--with their noses pointed straight up and their descent engines on idle.
As the increasing air density starts to slow them down, the engines are used to control their rate of descent in order to prevent surface heating from exceeding under-surface design limits.
Eventually, the speed in the increasingly-dense atmosphere will have diminished (a) in the case of the spaceplane, to where the angle of attack can be reduced to cruising attitude and the engine shut down (b) in the case of the Soyuz, to zero, and the descent engine used to reduce the vertical speed to parachute deployment rate, prior to landing--with legs extended to protect the engine from aft-first landing damage.
Well, that's it, for the moment....

tim_perdue · 2003-04-04 11:59:43

Sounds like it would take a lot more launch fuel, and result in a much heavier craft with more moving parts.

One big problem I see: if the descent engines failed, the craft would burn up on re-entry.

soph · 2003-04-04 12:19:28

I've talked about before the possibility of using an NTR-that could carry fuel into orbit, and slow down before reentry. Turn off the reactor when the descent begins, and glide down to landing.

dicktice · 2003-04-04 12:49:02

tim_perdue:
(Regarding fuel.) The present existence of the ISS is what makes this scheme possible--where fuel can be accumulated, stored, produced in orbit from water (stored as ice). Rocket-engine hardware being relatively lightweight, returning spaceplanes would get progressively lighter on the way down as fuel is burned--becoming lightest at burnout, when the proper density-altitude is reached for subsonic glider-flight, followed by a conventional runway landing.
(Regarding power failure.) Restartable H2/O2 engines have proven very reliable, from Apollo onward...at least as reliable (I assume?) as the present method involving 1st-generation ablative-tiles...at least in their present condition.
This scheme is an interim proposal, intended to support completion-to-full-utilization of the ISS; to avoid its being placed "in mothballs" while NASA et al. contemplate giving-up civilian manned space exploration in favour of exclusively government "defense" programmes.

dicktice · 2003-04-05 10:06:47

I've talked about before the possibility of using an NTR-that could carry fuel into orbit, and slow down before reentry. Turn off the reactor when the descent begins, and glide down to landing.

Bravo, Soph! My intention precisely--but, for now, use off-the-shelf technology to accomplish this as soon as possible (like yesterday)....

MarsGuy2012 · 2003-04-10 23:18:03

I'm no engineer so this idea is probably full of holes, but here goes.

Let's build a spaceplane with a moderate heat shield and load it with a moderate amount of fuel. Instead of using a direct entry it could skip along the upper atmosphere slowly shedding some of its speed while only moderately heating its heat shield and not burning it away. It could maintain a high altitude by slowly pitching back until it neared a stall. I would guess that this would take several orbits to accomplish. At that point (hopefully after shedding much of its velocity) the engines would kick in and burn for a much shorter time. Then the reentry would happen just like dicktice described.

I don't know much about hypersonic upper-atmospheric flight, but it seems to me that aerodynamics would still work up there. OK...anyone with half a brain can now chew up my plan and spit it back in my face. I'll wear the shades to protect my eyes from the chewed up shrapnel.

soph · 2003-04-11 04:31:24

Wouldn't work-skipping creates a lot of stress. The best bet is to slow down in orbit, and then glide down.

clark · 2003-04-11 10:04:22

Not much of an expert on this, so here is a baisc idea:

The main problem with the shuttle tiles, the entire solution to reentry, is that it takes so darn long to reattach them to the shuttle. So much prep work goes into just this one piece of NASA technology, that it reduces turn around times, and creates a huge amount of opportunity for fatal errors.

That said, the system as designed works rather well. Shuttle goes up, shuttle comes down. Yet, couldn't we improve how this system is updated and repaired?

I think this more matieral sciences, but I would imagine a material that can be sprayed onto the Shuttle between each flight. The spray would be like Teflon, or whatever matieral would work, and would dissipate on reentry.

So every time the Shuttle needs to be launched, it just needs an updated and technologicaly sophisticated paint job.

Any matieral with high temp resistance that can be delivered in a spray form, then congeal into the final protective armor?

The idea is to reduce the need to continually replace the tiles.

dicktice · 2003-04-11 10:06:11

MarsGuy: You and I are are very close, in principle ... but skipping (as Soph states) is to be avoided because--like skipping a stone on the water--this will lead to instability followed by a "death-dive" straight down, and burn-up.
All it needs to work, is enough fuel aboard (obtained from the ISS prior to undocking) to control the rate of increasing density-altitude while you are slowing down from orbital velocity. Add just enough thrust, as you increase your aerodynamic angle of attack gradually to the vertical, to prevent overheating the (titainium metal?) undersurfaces as you loose height ... until your airspeed is slow-and-low enough to recover from what has by then become your maximum drag, vertically-stalled attitude (using the Russian fighter-pilot's technique of vectoring your thrust) to normal cruising flight attitude. Then cut your power, and glide to a normal dead-stick landing....

soph · 2003-04-11 15:40:17

clark, spray material may sound easy enough, but it can add up to quite a bit of weight in a launch, which means a lot of extra money, and less mass that can reach orbit.

This had been discussed at space.com, and i believe at one time spray material had been used on the SRBs.

MarsGuy2012 · 2003-04-12 14:58:01

OK dicktice and soph,

You both worry about tiles, heat shields, or spray material being to heavy to launch. What about all that propellant needed for a powered landing? Dicktice has been talking about refueling at the ISS. Where does the fuel come from? Is it shipped in from an ice rich asteroid? Is it launched with an expendable heavy lift launch vehicle? It seems to me that shipping extra fuel into orbit will be much more costly than burning up a heat shield.

soph · 2003-04-12 15:16:45

Well, if you used an NTR, the only expense would be more tankage, which is usually about 3% of the mass of your fuel. Due to the mass ratio of NTRs, you can sacrifice a little mass and still get vastly more payload than a chemical system.

If it is launched via heavy lift booster, it could be a huge tank of fuel, so it could last several missions. The payload gained by reducing the tile/heat shield would be worth the cost. And then there's the added safety.

dicktice · 2003-04-13 09:35:25

Mars Guy: I'm with Soph ... insofar as rocket fuel launched into LEO for storage in the vicinity of the ISS, would remain in the original tanks. The anti-slosh baffles inside the tanks may, as well, be designed in the form of rudimentary living-quarters partitions, for completion in orbit after being emptied of fuel. Assuming that Mars Direct spacecraft will be assembled in LEO, this could simply be a part of the overall plan. Hopefully, next generation launches will involve very little expendable hardware ... retaining in LEO everything possible, including the left-over fuel in 2nd-stage tanks parked in orbit. The rocket engines could either be left attached to the tanks, for self propulsion if desired for some purpose, or detached and returned by spaceplane to Earth for refurbishment and reuse. Ultimately, of course, water-ice from tether-accessed astroids inside Earth's orbit should be obtainable as a bi-product of mining them.

MarsGuy2012 · 2003-04-13 22:29:30

Soph,

I am totally with you on the NTR thing. I just think the public would say something like, "Linch the nuke lovers!!!". Or at least it would be a hard sell. The FAA would probably hold us up for years if we did it privately. I assume your talking about using the NTRs from the Earth's surface. I bet firing them up in LEO (for an interplanetary mission) wouldn't be that much of a problem, though.

Dicktice,

I like the idea about launching everything you can into LEO and leaving it all there. It is pathetic how we just throw away all these huge (expensive) rockets after just one use.

I've never thought much about designing fuel tanks with rooms built into them. Has there been much research about that.

Oh, that comment about Mars Direct spacecraft being assembled in LEO is way off. The whole point of Mars Direct is to avoid on orbit assembly.

One thing just came to mind about using powered decent. By the time powered decent vehicles finally get approval from congress and finally get designed and built there will be better heat resistant materials (and computer guidance) out there that might make powered decent less important or even obsolete. Just playing Devil's advocate. :angry:

dicktice · 2003-04-14 15:31:45

MarsGuy: Nice response ... gives me something to chew on.
If LH2 and LO2 tanks need internal anti-slosh baffles, they might as well be designed to serve the dual purpose of (1) slosh reduction and (2) basic partitioning suitable for attaching fittings such as cabinets, tables, washrooms, airlocks, etc. sent up separately in kit-form. (Old idea, whose time has arrived?)
I haven't read "Mars Direct" so I'm not familiar with the launch means proposed. I was thinking of Russia's Soyuz Rocket, which would appear too small in diameter for a Mars ship. And what about fuel? I assumed final "topping up" of the Mars ship would take place in LEO near the ISS.
Re. Powered descent: I was thinking of the space plane I saw proposed, here somewhere (www...?), to be towed by a Boeing 747. Skinned with titanium on its undersurfaces instead of being tiled or coated, it would be lighter and impact resistant. I imagined a fully-stalled, throttled-rocket controlled vertical descent re-entry, with conversion to subsonic gliding attitude at 50,000 feet (say), to be preferrable to the current hyperspeed ablation method, at least for LEO operations, for the near future. (The same space plane design should be suitable as well for mountain track launches....)
I intend to work more on this. See ya.

MarsGuy2012 · 2003-04-14 15:55:24

Dicktice,

Why haven't you read up on 'Mars Direct'? This is the 'New Mars' forum!!! Sadly I think many in here haven't read 'The Case for Mars', so grading on the curve you're not doing too bad. But tell me why. Why haven't you read 'The Case for Mars'?!?!?!

I'll assume your too busy saving the world or something so if you like I'll start a new topic with a quick summary of the Mars Direct plan. Just let me know if you want to see it.

dicktice · 2003-04-16 08:19:44

MarsGuy: A new Mars Direct topic is a good idea!
It's not in any bookstores, or our library, or the university, or advertised.... I just found out about Mars Direct when youse guys brought it up in your posts. This is a whole new world, that is nearly totally unknown out there in the real world. Mars Society PR is practically nonexistent, except for the converted like youse guys, don'tchaknow? IGuess I'll have to buy the book(s) when it/they arrive in the local used book store...?

soph · 2003-04-16 12:55:03

Mars Direct is explained in the most detail in Zubrin's _The Case for Mars_

MarsGuy2012 · 2003-04-16 20:50:39

soph,

duh...

It seems dicktice is having trouble getting a copy.

soph · 2003-04-16 20:58:02

I think he didn't know the title, because a 30 second Amazon search, and:

Case for Mars

dicktice · 2003-04-17 08:07:50

I think he didn't know the title, because a 30 second Amazon search, and:
Case for Mars

Right on, thanks Soph.

dicktice · 2003-04-17 08:55:28

A few days ago, I submitted what I called a "silly sounding scheme" for preventing bone loss during the Mars Direct (weightless) trip out, takin up to nine Earth months to get there or back. But I can't find it now, and therefore haven't learned if the idea is silly or not. So here it is, again:

Given, the Mars Direct spacecraft has no more than a twenty-foot inside diameter ... postulate a transverse centrifuge platform, shaped like a pieplate fifteen feet in diameter, on which up to four crewmembers can go to bed during each eight-hour sleep period. They sleep with their heads towards the centre, feet braced against the inside of the perpheral rim, suitably restrained from drifting off the platform while spinning. The spin-rate, such that 1/3rd-gee would be experienced at about 1/3rd-radius, I guess would be pretty fast. I wonder if someone hasn't already proposed something like this (pretty obvious) idea, for use in non-spinning habitats enroute to Mars...?

soph · 2003-04-17 08:58:39

The problem is that your feet would experience significantly lower G than your head.

Zubrin's idea is to have a tether attached to the front of the ship, with something non-essential attached (maybe a tagalong satellite). Spin the tether, and you generate significant G throughout the ship. If the tether fails, you haven't lost anything essential.

dicktice · 2003-04-17 09:32:07

No, no, Soph. Your head-bone is already thick enough (sorry, I couldn't resist that--nothing personal). It's at the centre, with your feet at the rim ... hopefully benefiting the legs and (decreasingly "higher up") supporting skeleton. Call it a proposed emergency alternative to the tethered, rotating two-component spacecraft you mention.
I just wondered if it would suffice--let's now say--if your "non-essential something" goes spinning off. (What nonessential would that be, I wonder?) In that case, the internal sleep-centrifuge might come in handy if it turns out to beneficial. The question remains: Is it...?

MarsGuy2012 · 2003-04-17 09:35:44

dicktice,

Here is the Mars Direct Home Page

If you don't have a copy of "Case for Mars" yet, just go here.

New Mars Forums

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#1 2003-04-04 11:24:11

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#2 2003-04-04 11:59:43

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#3 2003-04-04 12:19:28

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#4 2003-04-04 12:49:02

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#5 2003-04-05 10:06:47

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#6 2003-04-10 23:18:03

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#7 2003-04-11 04:31:24

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#8 2003-04-11 10:04:22

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#9 2003-04-11 10:06:11

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#10 2003-04-11 15:40:17

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#11 2003-04-12 14:58:01

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#12 2003-04-12 15:16:45

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#13 2003-04-13 09:35:25

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#14 2003-04-13 22:29:30

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#15 2003-04-14 15:31:45

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#16 2003-04-14 15:55:24

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#17 2003-04-16 08:19:44

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#18 2003-04-16 12:55:03

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#19 2003-04-16 20:50:39

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#20 2003-04-16 20:58:02

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#21 2003-04-17 08:07:50

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#22 2003-04-17 08:55:28

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#23 2003-04-17 08:58:39

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#24 2003-04-17 09:32:07

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

#25 2003-04-17 09:35:44

Re: De-orbiting from LEO revisited - How to avoid highspeed re-entry

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