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Samizdata, derived from Samizdat /n. - a system of clandestine publication of banned literature in the USSR [Russ.,= self-publishing house]

You would rather not know

I have seen numerous questions which come down to “If NASA had taken the wing impacts on launch seriously, the astronauts could have been saved”.

Unfortunately this is not true. I’ll work through the scenarios. Some have been covered reasonably well in the media; some not so well due to a lack of real understanding of orbital mechanics.

  • Why didn’t they have a docking collar?

The Columbia is the heaviest of the shuttles because it is the oldest. For that reason it performs many of the non-space-station missions. This one in particular had a Spacehab in the bay. The spacehab couples to the main airlock of the crew cabin. It also supplies an EVA lock if I remember correctly. What it does not do is allow for an International Docking Collar. There simply will not be room (or more accurately enough payload weight capacity or “payload mass budget”) for one on any flight doing really major non-station hauling.

  • Couldn’t they have gone to the space station if they’d known?

No. The space station is in an “orbital plane” tilted around 50 degrees to the Equator. Since KSC is at around 25 degrees latitude, a spaceship going into orbit there will be best off going into an orbit that is tilted 25 degrees to the equator. If you have a globe handy, look at the location of KSC in Florida. An orbit is a circle around the earth with the centre of the earth as its’ centre.

The Earth is about 24,000 miles in circumference. If you are standing on the equator, you must do a full rotation in 24 hours; thus you are travelling at about 1000 miles per hours. If you were to launch from there, in the direction the Earth is turning, you get your first 1000 mph for free. As you move further north or south, the “length” of your line of latitude gets smaller and smaller. You travel a shorter distance in 24 hours, so the velocity is lower. When you reach the pole, you just turn in a circle once a day but don’t actually go anywhere. Your velocity is 0 mph.

When a rocket takes off, it must go into an orbit; it cannot follow a line of latitude except if it is at the equator. So it not only gets a lower free boost the further it is from the equator; it can’t even use all of it. I’d really like to get into the velocity vectors but that would require diagrams and an assumption you have all had geometry. Instead, just think of the extreme case: if you wanted to launch due North, a “free velocity” in the due East direction is something which not only doesn’t help; it must be cancelled out.

So we now have an idea about why a particular orbital plane (actually a pair of them) is the “cheapest” for a given point on the Earth’s surface. If you are at KSC, it is about 25 degrees; if you are at a Russian launch site, it is more like 55 degrees or higher.

When a shuttle is going to the ISS, it must do a “plane change”. This is most efficiently done during the boost phase. The shuttle rolls onto an azimuth for that orbit and boosts up along the East coast of America. But this is costly; it is not getting the full use of the “free velocity” it would have gotten if it instead rolled onto a 25 degree azimuth. It has to replace that lost factor by burning more fuel. A longer burn means more fuel; more fuel means more fuel to lift that fuel and so forth… this is what is known as the rocket equation.

Carrying more fuel means less of the total mass budget is available for payload.

Once you get into orbit, a “plane change” maneuver is just about the costliest (in terms of fuel) thing you can do. You are travelling at 18000 mph in a very heavy vehicle in a “straight line”. Remember “things in motion tend to stay in motion”. There is a lot of momentum. If you want to go from 25 degrees to 50 degrees inclination, you have to fire your engines at right angles to your direction of motion. You have “turn” your entire orbit. It is almost “cheaper” to land and re-launch than to make that change. It is certainly beyond the abilities of any of the shuttles.

But that is only the first maneuver! The ISS is in a higher orbit. So you also have to do a burn that raises the apogee or high point of your orbit. This is a “Transfer Orbit”. When you next reach perigee, you have to do another burn to raise the perigee. This is a “Circularization burn”.

Oh, yeah… you will have to then be in an orbit slightly above that of ISS so you’ll rendezvous with it within a few days. Then you do minor orbital changes and carry out the rendezvous and docking.

If this all sounds like a nonstarter… you are correct.

  • Well, couldn’t they just sit tight and be rescued?

No. They have limited food and water, but most critically, they have limited Oxygen. Whether the margin left after that 16 day mission was in days or a couple weeks I don’t known. I guarantee you it was very finite.

Shuttles are not “launch on demand” reusable vehicles. They are more “re-buildable” vehicles that are extensively refurbished after each flight. There might have been one already stacked (I haven’t checked the status) but even so, it would take days to get it out to the pad; days more to do a rush checkout job… and they still wouldn’t have the computers set up for the mission. I do not know how hard they can push that. Maybe weeks if they took lots of risks. Shuttle flight software used to be scheduled and tested over a period of many months in advance. They have in recent years done some “rapid” re-profiling of missions, but at the best I think we are talking 4-6 weeks.

Not soon enough I’m afraid.

  • Couldn’t we have asked the Russians to rescue them?

The Russians had an unmanned, full cargo ship on the pad. But the Progress vehicle is discarded. It has no re-entry system. The Russians currently build 2 Soyez per year. None were on the pad to my knowledge. Even if they were, a Soyuz holds 3 persons. You are going to need at least one inside to deal with on the spot issues. So best case, you can draw lots and save two… but ooops… There is only one EVA suit. So I guess you save one guy and wave to the rest.

  • Couldn’t one of the Astronauts have gone EVA and fixed it?

No. It’s conceivable the EVA could have been carried out; however one astronaut spokesman has pointed out the risk of the inspector causing damage. And if he finds “a situation”… there is no means of in-orbit repair.

  • Couldn’t they have just been really gentle on re-entry?

Doubtful. The re-entry glide path is tightly constrained. Too shallow and you skip a number of times and then when you dig in you dig deep; too deep and you burn up. Like the three bears, you have to get the one that is just right. Perhaps they could have avoided the S turns, started re-entry further out and stayed wings level… but my level of hope for that is rather low. It’s probably the option they would have tried.

It comes down to this. If they had known from immediately after launch, those seven people would have spent their last 20 days of life facing certain death. Instead they enjoyed themselves immensely and died instantly doing exactly what they wanted to do.

Who could ask for a better way to go?

11 comments to You would rather not know

  • G.Haubold

    Dale: Great stuff on the orbital planes, transfer orbits, etc.

    There are a few minor details we disagree on: (1) my understanding is that the Columbia was so heavy (as the oldest orbiter) that it couldn’t reach the ISS even if initially targeted there, (2) I think it’s conceivable that a rush launch of the Atlantis might have gone up in as short a period as a week or two (it was being readied for a 3/1 launch) with a crew of two to leave room for passengers, but that would have put two additional pilots at grave risk, and (3) I’ve read that the orbiter could have been angled as much as ten degrees to port around its yaw axis to shield the left wing from some of the reentry heat.

    None of this changes the fact that the Columbia was probably doomed from the launch onward, but it seems to me that the ground-bound engineers didn’t put much effort into checking into the potential damage to the left wing TPS. Even if there wasn’t anything obvious that could have been done, I still fault them for not trying.

  • How do we know they didn’t try? From what I’ve read here and elsewhere, in particular on the extreme fragility of the tiles, it seems like they probably had a good idea what had happened. But as Dale points out, there was nothing they could do about it.

    Let’s not forget that this is NASA we’re talking about. I’d be willing to bet that the people in charge knew what was going to happen, but kept it quiet in the hope that the Columbia might somehow make it down safely after all.

  • G.Haubold

    Lying is never good strategy to enhance credibility. Dittemore has repeatedly stated that NASA and outside experts looked at the potential for wing damage and decided that it was a minor issue and the reentry proceded normally. I believe his statements have been truthful, but you never know.

    As regarding damage to the TPS, that occurs on EVERY FLIGHT, and anywhere from 30-100+ tiles have to be repaired or replaced before the orbiter can fly again. It’s been considered a minor issue and a manageable risk, until now (NASA took the same approach to problems with the O-ring seals before the Challenger).

    I’m not sure that it’s possible to angle the orbiter 10 degrees to the left to try to put more thermal load on the right side – but there’s no evidence the procedure was either discussed or tried.

  • Your faith inspires me.

    The folks at NASA are more interested in a safe ending to a space flight than they are *any* other factor. Do no science, go nowhere, achieve nothing, but come back alive. All else is gravy.

    Anything that could have been done, would have been done. If the flight engineers thought, at the time, that the foam impact on the wing presented a significant danger, any and every possible step would have been taken to mitigate that risk to produce the best likelihood of the safe return of the astronauts to Earth. Even if that meant abandoning Columbia in orbit. (Not that such a thing was a feasible solution in this instance; it’s more a statement of resolve.)

    Engineering judgment is no match for hindsight. The professional definition of “possible step” does not match the layman’s. And the problem with taking risks is that sometimes they don’t pay off.

    Just my personal opinion.

  • Paul Marks

    I am no expert, but I have long thought that the Shuttle is an underpowered and rather flimsy vessel.

    If what you write is true then the Shuttle is worse than I thought. If you have 20 days after taking minor damage (or whatever really caused the end of the vessel) and the bottom line is “we can do nothing, we are doomed” (which is basically what you have written), then the Shuttle is crap.

    If space travel is going to depend on being in exactly the right orbit (because the engine is so crap it can not do anything) then these oversized fireworks are of limited use. Either we take on the Greens and put proper engines into space craft (you know what I am talking about), or we may as well forget the whole thing.

    Also as Space is a hostile environment (with even the radiation levels being higher than was thought only a few years ago) the age of “thin hull and hope for the best” has got to end.

    For many years the idea of space planes to get to a space station has been talked about (using the atmosphere to the extent it can be used and then for the final push using something else), but certainly once a plane is at the station the vessels built there (at the station) must be strong craft with decent engines – not the sort of ships we have now.

  • G.Haubold

    Yep, the shuttle is crap.

    It was supposed to be a cost-effective space truck, but the ambitious design spec’s were too expensive to reach. So they built a dog.

    Most of the satellite action is at geosynchronous orbit, up at 22,700 miles – but the shuttle can’t get there.

  • Dale Amon

    Yes, the shuttle is a white elephant. But not necessarily more dangerous than any other 1970’s spaceship would be. We are for the moment stuck with chemical propulsion for Earth to Orbit transport. That will change over time. There are other ways to do it, but they require large capital investments. Large infrastructures investments are possible, but only if there is extremely low risk in the market. Translation: we have to use what we’ve got to build the market in LEO to the point at which international finance will feel safe in building a beanstalk, a launch loop, a tether system or whatever.

    The nuclear rocket battle will be won someday, but not any day soon. Our energies are best placed in getting wholly and permenantly space based nuclear powered vehicles. If Bush pushes for the nuclear-electric engine, he will give us the solar system.

    I’m most interested in finding paths that lead out of the cul-de-sac we are in. One has to have a very deep sense of pragmatism and a serious machiavellian streak to have any hopes of succeeding in this world that is and with this hand we have been dealt.

  • G.Haubold

    Isn’t it possible that we’re trying to push the technology past what it’s capable of at the moment?

    Kind of like canoeing across the Atlantic. Sailing to North America from Europe was never very safe, but sturdier boats and better sails made a real difference for Columbus and everybody that followed.

  • mojo

    The shuttle’s limitations bleed over, too. The ISS is in a dangerously low orbit, one where the edge of the atmosphere forces a stabilization burn every so often to prevent reentry. Why? Because the shuttles can’t make it to a better altitude for large structures.

  • Chris Connor

    RIP those who unfortunately passed away.

    Long live NASA and its Space Programme

  • Dale Amon

    To be fair, the shuttle limitations are a matter of a complicated trade off. Since the most efficient orbital plane from KSC is many degrees different from that of Baikonur, the ISS is in a tradeoff position so that both launch systems can reach it with reasonable efficiency. Fuel used for plane change cannot be used for getting a higher orbit; fuel used in either means less payload to the final orbit. As much as some complained about the tradeoff in the orbital parameters, I suspect they are silent now because without the russians the ISS would be f****d right now.

    If you want more payload in a high inclination orbit at a higher altitude, you can only get it by making the structures lighter, the fuel tanks bigger, or the engines more efficient.

    We’re already running LOX/LH engines which is the most efficient *reasonable* fuel; scraping a few more percent efficiency out of the SSME’s means making pumps run at higher pressure/lower margin, putting in variable expansion bells, and other things… all of which are asking for Cat 1 failures on an engine that size with current technology. This is not to say these items are slowly improving in an evolutionary fashion. The HP pumps are much better than what was around in 1981.

    So, yeah, it would be nice. But its’ already a huge vehicle flying with tight operational margins.

    I think next generation we go to big cargo ships and small passenger ships.