Question General Spaceflight Q&A

[IronRain]

The space station flies -XVV so that the heatsheild of the shuttle is protected from MMOD impacts. Several times windows or radiators have been damaged by MMOD and the decision was made that this is preferable to the rather fragile tiles.

Does it has any effect on the station self?

 

[garyw]

None that I am aware of. The Shuttle docks with the station in +XVV attitude then slowly rotates using CMG's to the -XVV attitude. This does take several hours.

Don't forget that when STS-133 docked the oscillations on the docking interface were so bad the ISS did a 'backflip' and it took sometime to sort it all out.

Of course, at no point was the ISS out of control or out of communication and the turn rate was so slow it wasn't felt onboard.

 

[neutronium76]

Hello. Just a noob and probably stupid question: What happens if ALL SSMEs fail i.e stop at the very early stages of the ascent? Can the SRBs provide enough thrust to lift the shuttle and the ET? And vice versa: what if the SRBs fail during the early stages of ascent? Not STS-51L type of failure. Just engine cut-off. I am talking about the early stages of launch from T+0 up to T+60''-+70''sec.

Another stupid question: Whould it be possible for the shuttle not to throw away the ET at MECO and cary it to LEO where another unmanned vehhicle with H2 and O2 awaits and then refuel the ET and then have enough fuel for a trip to Mars or moon? Maybe the shuttle could carry a lander in its payload compartment.

End of stupid questions.

 

[Star Voyager]

Regarding engine failure:

-if the SSME's cutoff, (this is what I would personally do, not sure if this is procedure) I would jettison the SRB's and the ET immediately and try to ditch as close to the Cape as possible.

-if the SRB's cutoff, the crew would have to do an RTLS after a manual jettison of the SRB's.

 

[Urwumpe]

Hello. Just a noob and probably stupid question: What happens if ALL SSMEs fail i.e stop at the very early stages of the ascent? Can the SRBs provide enough thrust to lift the shuttle and the ET?

Yes, the SRB provide almost 94% of the thrust during that phase, because the SSMEs become more effective at higher altitudes. The SSMEs are just ignited already on the ground to check if they operate properly before igniting the SRBs.

If the SSMEs fail all, you would have to wait until SRB separation for actions. The ET would then be separated the remaining propellant in the Shuttle propellant lines would be dumped (about 2 tons of mass) and the crew would try to bail out, because they couldn't reach any landing site in such a situation. It is a very risky maneuver, because separating a nearly full ET is not without danger, it could tumble and hit the shuttle during separation, but you can't glide with it.

And vice versa: what if the SRBs fail during the early stages of ascent? Not STS-51L type of failure. Just engine cut-off. I am talking about the early stages of launch from T+0 up to T+60''-+70''sec.

The SRBs are solid propellant rocket motors, such motors can only fail if they explode. They have all their propellant already in the combustion chamber, once ignited, they keep on burning until the run out of fuel or the combustion chamber fails and the pressure rapidly drops, which then slows the chemical reaction to a halt.

And if this happens on a SRB, this would be fatal.

Another stupid question: Whould it be possible for the shuttle not to throw away the ET at MECO and cary it to LEO where another unmanned vehhicle with H2 and O2 awaits and then refuel the ET and then have enough fuel for a trip to Mars or moon? Maybe the shuttle could carry a lander in its payload compartment.

Carrying the ET into LEO would be possible, and there are some plans to do that, but refueling the ET is not helping you there: The SSMEs can't be ignited in-flight, they can only be ignited on the ground, because they are really sensible and require strict temperature limits for ignition. Once a SSME cuts off, you can't ignite it again - even though the ignition system of the SSME is actually electric and could permit it.

The ignition sequence of a SSME is pretty complex and really a high art of engineering, it depends on the oscillations of thrust and fuel flow in the engine, and augments the pressure oscillations by carefully timed valve operations. If the temperature or pressures inside the engine are not right, the timing of these oscillations and the timing of the valves will not fit, also if parts of the engine are not pre-cooled for ignition, they would overheat and get damaged before enough propellant flows through the heat exchangers to cool these parts. Or you could get thermal stress in a valve, that is not properly cooled and gets in contact with the cryogen propellants, making the valve to contract unevenly and get stuck.


---------- Post added at 10:14 AM ---------- Previous post was at 10:11 AM ----------

-if the SSME's cutoff, (this is what I would personally do, not sure if this is procedure) I would jettison the SRB's and the ET immediately and try to ditch as close to the Cape as possible.

In the real world, you would then be damaged by SRB exhaust, also you would be likely too slow for a proper glide and crash. Ditching is also no option, you would normally bail out in flight. The Shuttle doesn't like ditching, as experiments of NASA have found out.

-if the SRB's cutoff, the crew would have to do an RTLS after a manual jettison of the SRB's.

SRBs can't cutoff without destroying the whole stack in the process.

 

[DaveS]

Hello. Just a noob and probably stupid question: What happens if ALL SSMEs fail i.e stop at the very early stages of the ascent? Can the SRBs provide enough thrust to lift the shuttle and the ET? And vice versa: what if the SRBs fail during the early stages of ascent? Not STS-51L type of failure. Just engine cut-off. I am talking about the early stages of launch from T+0 up to T+60''-+70''sec.

1st part: Well, yes. But the entirely full ET would smash into the orbiter upon ET sep and completely destroy orbiter.

And don't think about bailing out with the ET as the orbiter is upside-down and bailing out requires the orbiter to be in a stable gliding flight. And the ET reacts very badly to being subjected to aerodynamic heating below 265,000 ft (79.5 km) as the LH2/LOX will then begin to boil excessively to point the pressures exceeds the ET structural capacity.

2nd part of the question: Any type of SRB failure is catastrophic. The sudden loss of thrust from the SRBs would destroy the orbiter due excessive aerodynamic loads.

Another stupid question: Whould it be possible for the shuttle not to throw away the ET at MECO and cary it to LEO where another unmanned vehhicle with H2 and O2 awaits and then refuel the ET and then have enough fuel for a trip to Mars or moon? Maybe the shuttle could carry a lander in its payload compartment.

Not possible. The SSMEs are not restartable once shut-down. Also, the orbiters were specifically designed and built for the environment in Low Earth Orbit (LEO), not deep space.

 

[neutronium76]

Carrying the ET into LEO would be possible, and there are some plans to do that, but refueling the ET is not helping you there: The SSMEs can't be ignited in-flight, they can only be ignited on the ground, because they are really sensible and require strict temperature limits for ignition. Once a SSME cuts off, you can't ignite it again - even though the ignition system of the SSME is actually electric and could permit it.

The ignition sequence of a SSME is pretty complex and really a high art of engineering, it depends on the oscillations of thrust and fuel flow in the engine, and augments the pressure oscillations by carefully timed valve operations. If the temperature or pressures inside the engine are not right, the timing of these oscillations and the timing of the valves will not fit, also if parts of the engine are not pre-cooled for ignition, they would overheat and get damaged before enough propellant flows through the heat exchangers to cool these parts. Or you could get thermal stress in a valve, that is not properly cooled and gets in contact with the cryogen propellants, making the valve to contract unevenly and get stuck.

Would it be possible then NOT to completely shut down the SSMEs but let them burn at say 10% of their total thrust or even less (and retroburn some RCS thrusters to counteract the forward propulsion) and then do the refueling? I am just trying to figure out ways of interplanetary travel using the Orbiter with minimal modifications in order to reduce the cost of developing a new type of spacecraft. But I presume that all this has already been thought in the past(and ruled out of course).
Anyway thanks Urwumpe and DaveS for your vary informative and simple explanation and for the trouble to answer stupid questions by a noob.:tiphat:

 

[garyw]

Would it be possible then NOT to completely shut down the SSMEs but let them burn at say 10% of their total thrust or even less (and retroburn some RCS thrusters to counteract the forward propulsion) and then do the refueling? I am just trying to figure out ways of interplanetary travel using the Orbiter with minimal modifications in order to reduce the cost of developing a new type of spacecraft. But I presume that all this has already been thought in the past(and ruled out of course).
Anyway thanks Urwumpe and DaveS for your vary informative and simple explanation and for the trouble to answer stupid questions by a noob.:tiphat:

No. minimum thrust for the SSME is something in the region of 64%. It is throttable engine but not that throttable! also thrusting at 10% until you meet your refueling target means you need to meet it the moment you are on orbit as the propellant reserves are very low.

Forget using an Orbiter for interplanetary travel. It is not worth it, not built for it and you are dragging a lot of hardware you don't need.

The two major problems are that the Orbiter was built for the thermal conditions in LEO and doesn't have the resources for anything more than a two week trip into LEO. Endeavour and Discovery can stretch that thanks to the Shuttle-Station Power Transfer System. Atlantis doesn't have that so her trips to the ISS have always been around 12 days.

12 days doesn't get you very far from Earth.

 

[Urwumpe]

Additionally to what garyw said: Close to MECO, the engines are already close to the 64% throttle and still the whole shuttle accelerates at 3g! You can't counter that by RCS, not even for a split second.

Also, the three SSMEs produce about 80% more thrust per kg propellants as the RCS, and can even at minimum thrust consume about 400 times more propellant as the whole forward RCS. Refueling the ET takes a few hours, even when the SSMEs are not at the same time consuming propellants at a very high rate. The fuel in the forward RCS tanks is only good for about five minutes of constant pulsed operation (you can't fire the RCS thrusters without breaks, they would overheat otherwise)

The Shuttle is not designed for flying past 700 km distance to Earths surface. This doesn't mean it is a bad vehicle, it is great in this region. If you want to go interplanetary with the Space Shuttle, you can use it for assembling a interplanetary spacecraft in low Earth orbit, that is what the Space Shuttle is pretty much designed for.

Endeavor could stay for about 25 days in orbit, with all options used - that would be enough time in theory for a short lunar mission. But there is then one big problem: The heat shield isn't designed for the speeds you get during lunar returns. It is already at the limits if the Space Shuttle returns from the 600 km high orbit of Hubble. If the heat shield is pushed beyond its capacity, the tiles simply fall off, because the inside of the tiles is getting too hot. I am not sure what the limit was, maybe 350°C, maybe already 250°C. Also, the aluminum structure of the shuttle gets already soft from temperatures of 200°C on, but it is behind an insulating blanket between ceramic tiles and structure.

You would need a completely different spacecraft for such missions.

 

[Dambuster]

Just a question: in this video at around 3:25, I can see what appear to be streaks in the SSME flames. What are these, and why are they there? I had always assumed that the SSMEs were meant to give quite a 'clean' (whatever that means ) exhaust.

 

[diogom]

I'm not sure, but it could be effects of the SSME throtteling up back to full power after Max Q. They're quite similar to the ones you see at SSME ignition.

 

[Krikkit]

Just a question: in this video at around 3:25, I can see what appear to be streaks in the SSME flames. What are these, and why are they there? I had always assumed that the SSMEs were meant to give quite a 'clean' (whatever that means ) exhaust.

http://www.youtube.com/watch?v=cKPqomW5kDI

My guess is that the fuel mixture went out of balance for a split second. I think the bright orange is an excess of hydrogen, which is normal because they always put more hydrogen in than needed to bond with the oxygen to absorb the heat and increase the mass flow.

-----------edit------------------

After watching it again it kind of looks like it could be debris hitting the plum and burning up.

 

[Urwumpe]

That was a piece of debris, if you look more careful, the streak starts downstream of the engine and not inside it. A small change in mixture ratio towards hydrogen rich makes the exhaust more violet - perfect mixture is invisible.

And nice progressive metal soundtrack, BTW.

 

[ElPelado]

Small question: have they already used the airlock in JAXA's lab??

 

[garyw]

Yes, it's been used but I have a feeling you are asking if it's been used for EVA's? in which case the answer is no, it's too small.

 

[Orbinaut Pete]

Small question: have they already used the airlock in JAXA's lab??

Yup - it was used to deploy the JEM RMS SFA (Japanese Experiment Module | Remote Manipulator System | Small Fine Arm) in March 2010.

Hi-res version.

Hi-res version.

Hi-res version.

Hi-res version.

In the future, there are proposals to use the JEM airlock to deploy cubesats, deploy and retrieve free-flying remote cameras, and deploy small re-entry capsules. :thumbup:

 

[ElPelado]

Oh no, I wasn't asking about EVA's.
I was asking about using it like Orbinaut showed in the pictures.

So, that was the only time?
No experiments where transferred from the inside, or the opposite way?

And what's that hand for? i can understand that it will be used for handling smaller things, but what exactly? where will it "park" when it's not being used (or when the bigger hand has to be used)?

Thank you!!

 

[Orbinaut Pete]

Oh no, I wasn't asking about EVA's.
I was asking about using it like Orbinaut showed in the pictures.

So, that was the only time?
No experiments where transferred from the inside, or the opposite way?

And what's that hand for? i can understand that it will be used for handling smaller things, but what exactly? where will it "park" when it's not being used (or when the bigger hand has to be used)?

Thank you!!

No experiments have been transferred via the JPM airlock yet, but HTV-3 will bring up some CubeSats in January next year, which will then be deployed using the big arm (see page 4 of this PDF presentation).

As for the small arm's use, check out the image below (rotate 180 degrees for proper orientation - I have assumed this in the below description). The Exposed Facility (EF) is visible in the bottom-right corner. On the top of the EF, you can see lots of small box-like objects (I'm not talking about the larger ones on the side). Those small boxes contain all the systems that make the EF work (power, data, cooling etc). If ever one of those boxes breaks down and needs to be replaced, the small arm would do the job, since the big arm is too large.

The small arm is stored on the EF when not in use, and you can see the grapple fixture for the small arm in the image below, in the forward-left corner of the EF.

Hi-res version.

 

[garyw]

Pete any info on those JAXA re-entry capsules? sounds interesting! cheers.

 

[Orbinaut Pete]

Pete any info on those JAXA re-entry capsules? sounds interesting! cheers.

Here, and page 18 of this PDF presentation (<- this entire presentation is good reading in terms of ISS tech demos).