Question General Spaceflight Q&A

Urwumpe

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1. What is the emergency procedure in the case of rapid depressurisation? Are there things that seal shut the affected modules or something? How big would a hole in, say, a window need to be for a rapid depresurisation to take place?
Depends on how rapid the depressurization is. When the crew has many hours before it would run out of oxygen, the standard procedure contains locating the leak and seal it.

In cases, where only a few minutes would be left (similar to Mir), the crew would either attempt to seal the then known module from the rest of the station (for example Columbus) or directly flee to the Soyuz (or docked Shuttle) and wait for further orders after sealing the hatches.

A hole does not need to be very large, 2mm diameter is enough for causing trouble, but the large volume of the ISS means it would require quite a large hole (more than 1 cm) for causing instant rapid depressurization.

Locating leaks and reacting to them is part of standard ISS training.

2. How big are the interior of these modules? Does it tend to get cramped up there?
The modules have generally 4.5m diameter on the outside and the inside is about 2.2m x 2.2m across. How cramped it gets depends on many factors, most important:
- Age of the modules: Older modules have more stuff stowed and experiments installed.
- Activity: Where more work is done, more stuff likes to be stowed inside the walls

The most cramped part of the ISS is most likely the FGB, which is used as "space attic" currently, followed by the service module.

3. Is there a definate front and back of the ISS? Do they tend to point one direction prograde most of the time, or do they do a flip-the-coin (as impossible as that would be on the ISS) and say "Ha, looks like the Ruskies are being blasted by the Sun for the next quater orbit"? Not that I have anything against Ruskies :)
There is a standard orientation of the ISS, putting the Russian modules into the aft direction of flight because of their maneuver capability and the US module in front.

This orientation is also used for designating the names of the payload racks: Forward, Aft, Port, Starboard, Overhead and Down.
 

Urwumpe

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Whats with the air data probes, there simulated in SSU and shuttle fleet, but what do they do?
They measure temperature, angle of attack and static and dynamic pressure. With this data, it is possible to calculate pressure altitude and equivalent air speed (EAS), a measure of air speed which directly relates to the flight behavior of the Shuttle (the shuttle always behaves the same as long as you fly at the same EAS).

This data gets used for making the navigation more accurate, as it only has inertial, TACAN and GPS data available before the deployment of the air data probes. All three are only accurate to a few meters (GPS around 10m, inertial and TACAN around 50m), while the air data probes are accurate to a few feet in altitude.
 

Urwumpe

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So they are used in landing? i thought it would be pretty pointless using them in space.
Yes - only for landing and only at velocities below 5000 ft/s or 1525 m/s or Mach 5.
 

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Because of my trip to Bonn on Wednesday (to the House of History), I'm reading about Ulf Merbold's flight on STS-9 (because they had one exhibit showing Sigmund Jähn's Spacesuit, Merbold's Shuttle Flght plan and even a moon rock from Apollo 12).

On Wikipedia I read about the crasing of the two GPC's before re-entry. The text said:

Wikipedia said:
During orbiter orientation, four hours before re-entry, one of the guidance computers crashed when the RCS thrusters were fired. A few minutes later, a second crashed in a similar fashion, but was successfully rebooted. Young delayed the landing, letting the orbiter drift. He later testified: "Had we then activated the Backup Flight Software, loss of vehicle and crew would have resulted." Post-flight analysis revealed the GPCs failed when the RCS thruster motion knocked a piece of solder loose and shorted out the CPU board.
My questions:
1.)Why would activating the BFS having resulted in loosing the Shuttle?
2.) What had happened to the APUs? I heard, that the crew got an Underspeed Warning after landing, but as Wikipedia says:
Wikipedia said:
The leak was later discovered after it burned itself out and caused major damage to the compartment.
And a third question: In the Space Shuttle Mission 2007 Simulator I saw, that there is a field of buttons above the commander's seat. All in all 25 buttons, 5 for each GPC. And on the right side, the panel read "Vote". I once heard, that the GPC really kind of vote against each other. But what are these Buttons for?

Thanks in advance,
Lunar_Lander
 

Woo482

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yes thats true just don't ask me for a reason why they have to do that
 

Urwumpe

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1.)Why would activating the BFS having resulted in loosing the Shuttle?
2.) What had happened to the APUs? I heard, that the crew got an Underspeed Warning after landing, but as Wikipedia says:


And a third question: In the Space Shuttle Mission 2007 Simulator I saw, that there is a field of buttons above the commander's seat. All in all 25 buttons, 5 for each GPC. And on the right side, the panel read "Vote". I once heard, that the GPC really kind of vote against each other. But what are these Buttons for?
1. BFS is simplex - only one GPC can run it and all other GPCs are passive in this mode. When the BFS CPU would have failed by the same soldering error, the shuttle would have been without DPS during reentry - and even worse: Even without manual control, as the GPCs have to process the inputs. Switching back from BFS control to PASS (the normal avionics software) is no quick action and results in a long phase without control.

2. Two APUs had a fuel leak, which developed shortly after reactivating them for reentry. around touchdown, the first APU failed underspeed because the fire damaged the injector. A few seconds later another failed similar. The hydrazine fuel caused fires and small explosions inside the aft compartment, creating heavy internal damage, but as it all happened after landing, the actual danger was pretty low and the APU problem later fixed by improved design and more careful operations.


3. Thats no buttons, but just indicator lights. A few times each second, the GPCs can exchange a IO checksum word of 64 bits, which calculated from the IO channels of the GPCs. When multiple GPCs operate as common set (running the same software), each CPU compares the received word with it's own, and when it notices a difference, casts a failure vote against the other GPC. These votes get displayed in the 5x5 matrix (one row/column for each GPC). The diagonal elements have a white color, which is used for the indication of a self-fail vote.

When you see a failed GPC, the crew activity concentrates on the switches one panel above the matrix, making sure the failed GPC is deactivated.

Is it right that an RTLS (Return To Launch Site) only can be made after the SRB burnout?
That is not 100% correct - in theory, the SRB separation motors had been designed to separate the SRBs earlier than nominal, but the difference is not too great. I think it is around 100s for SRBs and was calculated to be 85s for LRBs.

The main problem is the mass of the ET. Like all will remember who attempted to launch the shuttle with unlimited fuel - it is impossible. So is the RTLS with too much fuel.

It may sound silly, but I do not understand the Attitude system used by space shuttle. What is LVLH?
Local vertical - local horizon

It means that the coordinate system has one axis pointing to or away from Earth (local vertical) and the other axes are inside the local horizon plane. This coordinate system changes with the position of the shuttle, but makes describing maneuvers simpler.

The X axis points in the direction of the velocity vector (or: Is inside the orbit plane), the Y axis points to the side and the Z axis points towards Earth. A prograde/retrograde maneuver would thus only require the X component of the velocity change vector to be defined.
 

ar81

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Empty ET is as heavy as a fully loaded truck.
I just can imagine what it would be to be a fish and then see a fully loaded ET falling to the sea during RTLS...

 

Urwumpe

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Empty ET is as heavy as a fully loaded truck.
I just can imagine what it would be to be a fish and then see a fully loaded ET falling to the sea during RTLS...
I would not be too sure, that the ET stays intact. At the end of the powered phase of a RTLS abort, the Shuttle gained again some velocity, is in a steep dive (800 feet per second descend rate or -245 m/s) and in the upper atmosphere.

Also, the Shuttle reaches 2.2G vertical acceleration (Nz) during the alpha recovery phase after ET separation, which is quite violent (2.5G is design limit of the Shuttle) and a sign of extreme dynamic pressure - the ET would get even worse dynamic pressure as it does not pull out of the dive.

The ET is not protected against high aerodynamic heating, which is proportional to dynamic pressure. Also, it can only survive high aerodynamic loads when flying controlled, but it will be tumbling after separation

I would be pretty surprised if the ET stays intact, I would expect fragmentation under these conditions.
 

orwellkid

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Is it right that an RTLS (Return To Launch Site) only can be made after the SRB burnout?

http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Intact_abort_modes
There are two reasons for this:

1. During an RTLS, you need to drain the ET to <=2% capacity. This is because the amount of liquid in the ET could cause the ET to swing back around and damage the Orbiter after ET sep.

2. Even though it's "possible" to abort prior to SRB sep, it's not done because any RTLS is executed at 2m30s minimum. This is partly for the reason 1 listed above, and partly so that the shuttle can gain enough altitude/velocity to safely glide back to the landing site.

Regards,

_O.K._
 

orwellkid

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Ghosts in the OMS engines.
 

Urwumpe

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Waste: What do they produce? How do they handle it?
All sorts of it you can imagine (packaging, wet trash, wet cloths) plus also the dirty laundry, which also not returned to Earth.

The waste is put into a Progress or ATV and burned in the atmosphere when the cargo ferry undergoes destructive reentry.
 
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