How Fast Can NASA Shuttles Really Travel in Space?

[noagname]

I don't know much about Nasa or their shuttles but i am wondering once they get into space can't they go as fast as they want, or is there something i don't know about.

 

[D H]

Vehicles in space still have the same mass as they had on the ground and are still subject to the laws of physics.

Think of it this way: If your conjecture were true we would have been able to send people to other stars as soon the we learned how to get out of the atmosphere.

 

[DaveC426913]

Vehicles in space still have the same mass as they had on the ground and are still subject to the laws of physics.

Think of it this way: If your conjecture were true we would have been able to send people to other stars as soon the we learned how to get out of the atmosphere.

That's not much of an answer. I would wager he knows we can't go to other planets and is looking for an explanation as to why.


noagname, the only way a spacecraft can go faster is by using fuel to propel it. The big limitation on the shuttle's performance is the amount of fuel it can take with it - which is very little on top of the huge amount it takes just to get to orbit.

Even if they filled the cargo hold with fuel, this would increase the liftoff weight of the shuttle, meaning it would use more to get to orbit, meaning they would use some of that extra fuel they brought, which would mean their outward journey would be correspondingly curtailed.

And we are sitll in a gravity well that we'd have to climb out of (using yet more fuel) to head away from Earth.

And if we wanted to explore once we got somewhere, we'd use more of that fuel to slow down at our destination.

And then we'd use more fuel to break out of orbit there, and again to get into orbit here on Earth.

That's the big limit: fuel.

 

[noagname]

well see if you forget about the amount of fuel
I am asking can the shuttle handle going at those speeds

 

[DaveC426913]

well see if you forget about the amount of fuel
I am asking can the shuttle handle going at those speeds

Yes. If the shuttle had a magical bottomless fuel tank, it could reach a speed arbitrarily close to the speed of light if it fired its engines long enough.

The occupants, other than getting bored or hungry, would experience no untoward effects. Indeed, they cannot demonstrate they are going fast at all except in relation to nearby objects.

 

[noagname]

just wondering what would happen after it hit the speed of light

 

[D H]

That's not much of an answer.

Well gee, thanks. Was that really necessary?

I interpreted the OPs question as "once a vehicle gets into space it is weightless. That means it can accelerate as fast as it wants and go as fast as it wants, or am I missing something?" The main thing he was missing was that the spacecraft still has mass. It still has weight too, and quite a bit. The actual weight of a spacecraft in low Earth orbit is nearly the same as the weight of the vehicle on the surface of the Earth.

noagname, when people say things are weightless in space, what they really mean is that things have no apparent weight in space. The actual weight of a spacecraft in low Earth orbit is nearly the same as the weight of the vehicle on the surface of the Earth. Even more importantly, the vehicle in orbit has exactly the same mass that it had on the surface of the Earth. This means that Newton's third law is just as restrictive in space as it is on the surface of the Earth.

Getting to low Earth orbit is just part of the battle. A vehicle has to flinish climbing out of the Earth's gravitational well just to begin going somewhere else in our solar system. As DaveC mentioned, that takes fuel. Then it has to use more fuel to get where it wants to go.

Here's where things get really nasty: There isn't any fuel in space. All of the fuel needed has to be carried up into space along with the vehicle. A lot of fuel is needed just to launch all the fuel the vehicle needs once it gets into orbit. The vast majority of the launch mass of a vehicle is fuel. Look at the Apollo missions. In order to send a fairly small vehicle to the moon we had to build the biggest vehicle ever built by mankind.

 

[noagname]

ok thanks

 

[phlegmy]

i've been told that if you get close to the speed of light and let's say you've loadsa feul left, so you burn it in hopes to accelerate further that instead of reaching [or exceeding] c, you'll just gain mass!
i do not understand what I've just said! I'm just repeating something someone once said to me!

 

[DaveC426913]

As you get closer to c, yes your mass will increase, and it will take more and more force to accelerate further (you will not experience any change within your ship - though the universe around you will start to look strange). You will never reach c but you can get artibitrarily close. If you then came back to your starting point, you would find that hundreds or thousands or even millions or years had passed.

 

[noagname]

ok then
so i am guessing that is how you would time travel

 

[DaveC426913]

ok then
so i am guessing that is how you would time travel

Well, it only works in the forward direction. You can never go home again.

i.e. You would accoomplish the same thing with a good suspended animation technology.

 

[noagname]

true

 

[rcgldr]

Getting back to the original question, it's an issue of fuel to payload. An "ideal" single stage rocket starts off as 91% fuel, the rest being the rocket and it's payload. The advantage of multiple stages is a reduction in the mass of final rocket stage and payload.

Space shuttles are designed to only achieve a low Earth orbit around 17,300mph (a bit more to get to the space station). There are 2 main stages and a detachabe fuel tank. The pair of solid rocket boosters can be considered to be the first stage. The shuttle also has 3 engines and that big oxygen / hydrogen tank that detaches (and burns up on re-entry). This is just barely beyond the outer edge of the atmoshpere.

In constrast, the Apollo spacecraft had 3 main stages, to get to the moon, then a lunar module and a lunar lander to return. The Apollo spacecraft went a bit over 24,000mph, not quite escape velocity, but enough to orbit far enough out to where the moons gravity had more force than the Earth's gravity. Fastest speed a man has traveled was around 24,700mph just before re-entry from one of the Apollo missions.

Sattellites, which are relatively small payloads, exceed escape velocity during launch.

 

[noagname]

wow
i am taking it that hydrogen is a very flammable fuel
why do they need that much fuel for re-entry couldn't they just use the Earth's gravity

 

[russ_watters]

Hydrogen, by mass, is the best fuel.

And they don't use much fuel for re-entry - just enough to re-shape the orbit so it crosses into the atmosphere.

 

[rcgldr]

Hydrogen is a very flammable fuel

liquid hydrogen + liguid oxygen are the most overall "efficient" fuels for rockets.

why do they need that much fuel for re-entry couldn't they just use the Earth's gravity?

Note I stated return, not re-entry. On the return trip, they only needed enoug fuel to transtion from a moon dominated gravitational pull to an Earth dominated one. My guess is the reason Apollo 10 had the fastest return speed was because the moon was further away from the Earth when Apollo 10 transitioned into the Earths pull, and so there was more distance to "fall" before re-entry.

 

[noagname]

ok
re-entry is right before they enter Earth's atmosphere
and return is heading to Earth right

 

[FredGarvin]

liquid hydrogen + liguid oxygen are the most overall "efficient" fuels for rockets.

In terms of what? Liquid hydrogen has a lot of pluses to it, but I could argue that H2 is the least efficient because its low density requires a large volume and thus requires large storage tanks. That increases vehicle weight and thus requires more fuel. It also requires, usually, jacketing of all of the piping that handles it in the cryogenic state. In terms of the overall system requirements, that's a killer.

 

[rcgldr]

liquid hydrogen + liguid oxygen are the most overall "efficient" fuels for rockets.

In terms of what?

Mass.

Liquid hydrogen has a lot of pluses to it, but I could argue that H2 is the least efficient because its low density requires a large volume and thus requires large storage tanks.

Higher density fuels are used for the first stage(s) of a multi-stage rocket, but the later stages, which the first stage has to accelerate, use lighter fuels. The final stages are almost always liquid hydrogen and liquid oxygen.

I'm not sure what fuel is used to slow down the shuttle for reentry. The small maneuvering thrusters use a fuel that doesn't have the storage issues of hyrodgen and oxygen, but it's toxic.

http://en.wikipedia.org/wiki/Rocket_fuel

Different fuels can be used for different purposes. Hydrogen Peroxide, 80% or more pure, only requires silver as a catalyst and is one of the few single component fuels. An example usage:

H2O2 usage.avi

 

[D H]

Higher density fuels are used for the first stage(s) of a multi-stage rocket, but the later stages, which the first stage has to accelerate, use lighter fuels. The final stages are almost always liquid hydrogen and liquid oxygen.

This is an overgeneralization. The Arianne 5 ECA and the Atlas V use LH2/LOX in their upper stages. Other rockets do not:

• US Space Shuttle.
  The Shuttle starts on the ground with a combination of solid rocket boosters and the Shuttle main engine, which does use liquid hydrogen and liquid oxygen. The main engine is essentially the first stage, augmented by the SRBs. After MECO (main engine cutoff), the Shuttle uses monomethyl hydrazine (MMH) for fuel and nitrogen tetroxide (NTO)for oxidizer.
• ESA Arianne 5G.
  The Arianne 5G, like the Shuttle, uses liquid hydrogen/liquid oxygen plus solid rocket boosters as a first stage and MMH/NTO in the second stage.
• Soyuz.
  The Soyuz rockets use RP-1 (kerosene) and LOX for their lower stages and unsymmetrical dimethylhydrazine (UDMH) and NTO in their upper stages.
• Proton.
  The Proton rockets use UDMH and NTO in all stages.

Hydrogen Peroxide is one of the few single component fuels.

Hydrazine is the most commonly used monopropellant. It has a specific impulse of about 230 seconds, as opposed to 160 seconds or so for hydrogen peroxide.

 

[mgb_phys]

Except H2O2 doesn't need an oxidiser so it is one of the few true monopropollent liquid fuels

 

[D H]

Hydrazine is also a true monopropellant. It decomposes into gaseous nitrogen and ammonia on contact with a catalyst. Hydrazine offers two advantages over H202: It has a higher specific impulse and the catalyst bed works at room temperature (or even lower). The disadvantage of any monopropellant is that it doesn't take much to set the monopropellant off. The flip-side of not needing a pre-heated catalyst bed means hydrazine is even more touchy than is H2O2.

The Shuttle uses monopropellant hydrazine to power its http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/apu/.

The hydrazine used as a monopropellant is plain old vanilla hydrazine, N2H4. This chemical is too unstable for use in conjunction with oxidizers. The hydrazines used with oxidizers are hydrazine derivatives rather than plain old vanilla hydrazine. Replacing one or two of hydrazine's hydrogen atoms with a methyl group yields monomethyl hydrazine (CH6N2) or unsymmetrical dimethylhydrazine (C2H8N2), respectively.

 

[rcgldr]

The final stages are almost always liquid hydrogen and liquid oxygen.

This is an overgeneralization. The Arianne 5 ECA and the Atlas V use LH2/LOX in their upper stages. Other rockets do not:

• US Space Shuttle.
  The Shuttle starts on the ground with a combination of solid rocket boosters and the Shuttle main engine, which does use liquid hydrogen and liquid oxygen. The main engine is essentially the first stage, augmented by the SRBs. After MECO (main engine cutoff), the Shuttle uses monomethyl hydrazine (MMH) for fuel and nitrogen tetroxide (NTO)for oxidizer.

• I thought the shuttle used liquid hydrogen and oxygen to achieve orbital speeds. Once at speed, the shuttle needs to be able to store the remaining fuel, and it only needs enough fuel to slow it down about 300mph->500mph or so to drop out of orbit, which is when the MMH and NTO fuels are used.
  
  

  Hydrogen peroxide is one of the few ... mononpropellants

  Hydrazine is the most commonly used monopropellant. It has a specific impulse of about 230 seconds, as opposed to 160 seconds or so for hydrogen peroxide.

  I didn't mean to imply it was the most popular, just that there aren't a lot of monopropellants, and H2O2 is something that more people are familiar with, at the 3% solution for household usage. Also, H2O2 is popular for use with "rocket powered" drag vehicles (although there aren't a lot of these either), like the bike in the previous video I posted.

 

[FredGarvin]

Hydrazene is one of the only ones that falls into both the mono and bi-prop categories.

Saying something is efficient in terms of "mass" is the equivalent of an incomplete sentence. It doesn't mean anything. You need to state that it gives the most X per unit mass. Just simply saying it is the lightest does not mean it's efficient.

Nice posts DH. I haven't thought about cat bed heaters since my rocket propulsion class.

 

[mgb_phys]

I didn't know you could use Hydrazine as a monopropellant - I suppose it doesn't need an oxiser if it isn't burning!

 

[Astronuc]

There's also diborane (B₂H₆), but that is really nasty stuff - much more flammable/explosive than H₂. Also the most effective in terms of chemical energy would be H₂ + F₂ with an Isp ~ 450 sec, but then the HF in the atmosphere would be no-no.

 

[D H]

I thought the shuttle used liquid hydrogen and oxygen to achieve orbital speeds.

The main engines bring the Shuttle to just shy of orbital speed. The Shuttle separates from the external tanks that supply LH2/LOX shortly after MECO (main engine cutoff). Since the Shuttle is not quite yet at orbital speed, the external tanks fall back to Earth. They hit in the middle of the Indian Ocean. The OMS provides the delta-V needed for orbit insertion, to get to the Station (or wherever), and to de-orbit.

 

[rcgldr]

Saying something is efficient in terms of "mass" is the equivalent of an incomplete sentence.

I sit corrected, left out the part about specific impulse. LH2 and LOX do seem to be popular. DH's posts cleared things up.

I wonder which (unmanned) rocket achieved the highest speed of the payload before utlizing slingshot effect off planets or the sun, and the parameters, like initial fuel to weight ratio, number of stages, type of fuel, ...

The only other tidbid I remember about the Space Shuttles, is because of Apollo 13, there's an active plutonimum button / thermal couple power supply in what's left of the lunar module at the bottom of an ocean (don't remember which ocean).

 

[rbj]

just wondering what would happen after it hit the speed of light

it doesn't hit the speed of light. even with all the fuel in the universe.

ok then
so i am guessing that is how you would time travel

we're all time-traveling. every second, we time-travel one second into the future.

you know, like the song Fly like an Eagle (Steve Miller Band): "Time keeps on slippin', slippin', slippin' Into the future ..."

Well, it only works in the forward direction. You can never go home again.

as is the case anyway... can't go back.