Dumb Space Shuttle question

[md2000]

@Chronos

Twice as fast is four times as much energy.

Doh! E=1/2 mv^2

But energy is proportional to quantity of fuel. That just makes the equation that much tougher. SSTO - single stage to orbit - is the holy grail. It is not simple with conventional engines. The X33 was supposed to be the newst tech and the next shuttle, but failed and was cancelled. The big issue was being able to build a tank/body that could handle the volume of fuel and still be part of the structure.

X-33/VentureStar - What really happened - NASASpaceFlight.com

[coremelt]

@md2000

Cost? When it’s hundreds of millions for an aircraft, and the market for people affording $8,000+ tickets (Concorde, anyone?) is relatively limited… and the airline industry has been close to bankruptcy for over a decade… who’s going to shell out? Without volume sales, the development costs would be too high per unit.
.

I meant as a cheaper way to get into orbit for launches, not as commercial transport. Not having to carry your own oxidizer the whole way should lead to cheaper cost per kg to orbit if the description of the SABRE is right?

[Fubaya]

The shuttle had 5 computers, four being used and one reserved as a backup. They were programmed in HAL/S and did have a very few very minor bugs over their lifespan. The shuttle only had a puny 1 megabyte of RAM, which sounds insane, but that’s all it needed. Russia’s Soyuz capsule flew for nearly 40 years on just 6 kilobytes until they upgraded it last year to… hold your breath… 2 megabytes. Apparently, playing Crysis in space isn’t high on anyone’s todo list.

[user_hostile]

@md2000

IIRC - At least one launch was scrubbed in the early days because the software crashed, or rather detected an error condition that required an abort. One article at the time marvelled at how they could isolate and fix the bugs within a week in a million lines of assembler code.

I vaguely recall the article discussing the tech, which by the time of the launches in the 80’s was considered primitive. There were 3 computers or 5 or something, and a majority had to agree for the system to work (in case the fault was a computer glitch or communication error by one of them to one of the sensors). On at least one occasion, one computer did not agree but the launch proceeded. I assume within a dozen flights they had worked out most of the problems.

I’ve not dealt with this issue in 15 years so I just realized my assessment was wrong. My bad. There have been actually quite a few problems, but none were would ever result in a loss of life or vehicle.

The Shuttle computer system has five computers. Four do the actual flight operations while the fifth stands by as a hot-swap in case one of the other four goes on the blink. A majority vote is used for the four computers (one does the work, while the other three vote on whether or not to approve the actions??? Too tired to look it up now.).

That abort occurred with the very first attempt at launching the Space Shuttle (I got up at like 3 am to watch it in California) The software didn’t crash, BTW. It was a problem with the backup computer not synching up with the other four. A slight technical story (Adobe file) describes what happens.

[Stranger_On_A_Train]

@coremelt

Is there a reason SABRE or other airbreathing to mach 5 / hybrid solutions aren’t being chased by other commercial companies or NASA? It would seem to have a lot of advantages, whats the downsides that prevent it being adopted?

Because they require technical breakthroughs in materials and scramjet technology that do not have foreseeable resolution. And while you save the weight of oxidizer that must be carried during atmospheric flight, you also incur the weight penalty and envelop restricitons of the lifting structure, which also has to be protected during reentry, all of this for the relatively small benefit that lift grants the craft. There is a large focus on aircraft-like launch vehicles just as there is a focus on ship-like spacecraft; because it is what we are familiar with, not because it makes technical sense, and the concept of a gliding vehicle is really a holdover from the A-12 bomber and X-20 DynaSoar skip-glide vehicles, which were not intented to go to orbit. The waste of carrying all that extra mass which offers no performance benefit above 200kft argues against its utility for space launch applications.

It is demonstratably possible to develop a SSTO vertical take-off craft using nearly off-the-shelf technology; the Titan II first stage was, in effect an SSTO (albeit with minimal payload), and that with the LR-87 engine which is 'Fifties-era technology with performance that is unimpressive by today’s standards. Some of the Phil Bono studies on SSTOs suggested that the Saturn S-IVB stage with a plug nozzle would be capable of being an expendable SSTO capable of carrying the Apollo capsule with a downsized Service Moduel for LEO applications, and the afforementioned SERV would have been capable of carrying Shuttle-class payloads along with a seperable personnel shuttle. With the use of high performance plug or aerospike engines, lightweight aluminum-lithium structure, and blunt-base reentry mode, a fully reusable SSTO should be well within the limits of existing technology.

The question remains regarding the need for a reusable SSTO. Current spaceflight demands and commerical markets currently don’t justify the cost of this development, though if Blue Origin succeeds with demonstrating cost-effective launch and rapid turnaround that may change. We will still need heavy lift vehicles, though, and for those low cost trumps complete reusability, which is where SpaceX (and the defunct Rocketplane Kistler) is hoping to demonstrate economies of scale. I personally think the Bob Truax sea-based Sea Dragon concept represents the best option for cost-effective heavy lift, with virtually no new technical development or high performance systems that stress material capability.

Stranger

[Chronos]

Quoth Stranger:
Pedantic nitpick; most of the heating does not come from any kind of friction, i.e. direct interaction between particles of the air and the tenuous atmosphere, but rather compression heating of the air forward of the vehicle (called ram pressure).

Most folks, when they use the word “friction”, mean any of a large general class of dissipative forces which resist motion. In this sense, ram pressure is a kind of friction.

Quoth fubaya:
Apparently, playing Crysis in space isn’t high on anyone’s todo list.

The mission computers (what’s needed for getting up and getting back down safely) are all very simple, but a typical Shuttle flight would also have a number of laptops on board for managing the various experiments they’re carrying. These are basically off-the-shelf and presumably could run modern games, though they probably don’t have time to.

[Fubaya]

@Chronos

… a typical Shuttle flight would also have a number of laptops on board for managing the various experiments they’re carrying.

The link I posted had an interesting bit about the radiation effects on those laptops. It’s pretty crazy to think your computer might quit working just because you’re at a certain spot above the earth.

With a ThinkPad 760XD laptop, two to three memory changes due to radiation occur during a shuttle flight to the Station, Klausman said. That number balloons up to 30 for a mission to NASA’s Hubble Space Telescope. The reason is that Hubble orbits about 150 miles higher than the station, where the radiation protection from Earth’s magnetic field is not as strong.

Designers also found out that laptops would crash when the shuttle passes through the “South Atlantic Anomaly,” which is an area where the magnetic field draws in to Earth, again offering less radiation filtering for spacecraft flying through it.

[Chronos]

Oh, and with regards to the X-15, the Pegasus rocket is designed on similar principles (launch from a high-altitude bomber, then fly with wings for a while until you leave the atmosphere) and can put payloads into orbit. It’s too small to carry humans, though.

[md2000]

@Fubaya

The link I posted had an interesting bit about the radiation effects on those laptops. It’s pretty crazy to think your computer might quit working just because you’re at a certain spot above the earth.

Another interesting story was how laptops and iPods crashed on the Tibet train. In the higher passes, the train gets over 13,000 feet. Most hard disks (early iPods were hard disks) the read/write head flies over the disk on a cushion of air, and over 12,000 feet the air is too thin for this effect, so the head scrapes the disk raw and removes the magnetic layer. Disks have very small pressure equalization holes, I understand, rather than being air-tight.

For the passengers, the compartments had oxygen pumped in, compensating for the low pressure with an atmosphere richer in oxygen. That doesn’t help the disks.

[Amblydoper]

Anyone having a difficult time understanding the finer points of space flight should play Kerbal Space Program. Its a simple game about putting a rocket into orbit.

[Leo_Bloom]

@aruvqan

…

I ask because I am not a rocket scientist, nor have I stayed at a holiday inn lately:D

[kenobi_65]

@Leo_Bloom

The ad campaign which Holiday Inn Express has run over the past few years feature people stepping into situations and offering expert advice. When asked, “are you a doctor / lawyer / whatever?”, they respond, “No…but I did stay at a Holiday Inn Express last night!” (The intended message being that choosing a Holiday Inn Express is a sign of extreme intelligence. )

[Dewey_Finn]

From Wikipedia, “In the mid-2000s, Holiday Inn Express began producing humorous television commercials featuring “average Joes” performing extraordinary activities that only experts would know. The concept attributes these exaggerated abilities to the fact that they “stayed at a Holiday Inn Express last night”. The campaign reflects the brand’s slogan “Stay Smart” which is still in use today.”

[user_hostile]

@md2000

Another interesting story was how laptops and iPods crashed on the Tibet train. In the higher passes, the train gets over 13,000 feet. Most hard disks (early iPods were hard disks) the read/write head flies over the disk on a cushion of air, and over 12,000 feet the air is too thin for this effect, so the head scrapes the disk raw and removes the magnetic layer. Disks have very small pressure equalization holes, I understand, rather than being air-tight.

For the passengers, the compartments had oxygen pumped in, compensating for the low pressure with an atmosphere richer in oxygen. That doesn’t help the disks.

At some point, one person I worked with was trying to find a hard-drive rated for use at 18,000 feet in the 90’s (weather station?). IIRC, there was nothing on the market at the time; don’t know if he ever resolved the problem. I heard IBM made a full size one for use in a vacuum, but I’ve not bothered to confirm this.

ETA: Full size as in the old 10 Megabyte hard drives in the IBM PC.

[SpyOne]

@brewha

You’re going to have a hell of a time getting back to earth if you do achieve orbit. Those jet engines are going to be useless without oxygen.

Not to mention how ill suited that shape is to re-entry.
When the space shuttle needs to re-enter the atmosphere, it moves so it is basically traveling bottom first, at it was specifically designed to effectively present the atmosphere with the same shape an Apollo Command Module had.