Question General Spaceflight Q&A

[garyw]

Not really. That would be an contingency deorbit.

the whole 'nice thing' about an AOA is that there is no engine firing required. You just coast back to KSC after ET separation - Remember at that point you are not in orbit, you are still in a ballistic arc until OMS-2.

Certainly AOA is used for major problems but normally its major problems noticed during the uphill ride. The flight rules list several such cases and I believe APU/Fuel cell and FES system failures (As in major failures) are on those lists.

 

[Urwumpe]

I remember reading somewhere that the shuttle doesn't open it's bay doors soon after MECO, that it waits a good while first. I know it's vague, but if it's true, why? Wouldn't opening the payload bay doors be one of the first things done on-orbit, to get rid of the system heat of the hydraulics, EPS, APU, OMS and MPS from the climb to orbit and OMS burns?

...Maybe, is it because they want to ensure all systems are working before they open the doors?

Shuttle Reference Manual didn't even mention the opening of the Payload bay doors as one of the post-MECO ops.

The opening of the Payload bay doors happens during the Post-Insertion (PI) checklist. Nominally you begin that task one hour after lift-off, with "CONFIG FOR PLBD OPERATIONS" (PI 1-14) and actually opening the doors at about 01:25 MET.

The PI checklist starts at 00:50 MET and thus directly after OMS-2. before you configure the payload bay doors, you have the following major activities:

• SPECIALIST SEAT EGRESS
• CONFIG GPCS FOR OPS2 (important since the payload bay door control software is in SM OPS2, also this is a very complex task, since it involves 5 computers at once)
• PL BUS ACTIVATION
• PRELIM MIDDECK CONFIG
• AFT STATION CONFIG (so you can also check that the payload bay doors open properly)

Between configuration for payload bay door operations and opening, you have:

• WCS CONFIG/ACT (the toilet, you really need it)
• SWITCH CONFIG/GALLEY ACT (If you get thirsty by now, you might like it)
• DON/CONFIG COMM (It is a bit loud in the Shuttle, so you better get this done soon, so you know what the person right next to you is saying)
• LOAD DAP A5 (configure the autopilot for the next maneuver)
• MNVR TO PLBD OPENING ATT ("maneuver to payload bay door opening attitude"; you can't do this in every orientation, you use "BIASED -ZLV +YVV".*)
• RAD ACT (the radiators are already activated before opening the doors - otherwise you could damage them)

*The exact attitude is defined in UNIV PTG as follows: Body vector is selected as 3 (-Z), Target is 2 (Center of Earth), Omicron angle is 280°. This means the shuttle Z axis is pointed as such that down (-Z) is towards the center of Earth, and Y is in the plane between -Z and orbit antinormal (-h) and then the shuttle is rotated clockwise around the target vector (towards center of Earth) by 280° (Defined in ORB OPS 7-33). Which in this case means: The shuttle flies wings level and with 80° slideslip to the left.

If +/- Y would be selected as reference body vector, the -Z axis of the Shuttle Coordinate System (down) would be used as second vector instead.

 

[Zamzara]

In Orbiter I can reach a Moron-TAL with one engine out from launch, and an ATO shortly after. This is with a payload set to 25 tonnes.

Clearly either the real life abort windows are rather conservative, or the simulated characteristics in Orbiter are a bit generous, does anyone know which?

 

[Urwumpe]

In Orbiter I can reach a Moron-TAL with one engine out from launch, and an ATO shortly after. This is with a payload set to 25 tonnes.

Clearly either the real life abort windows are rather conservative, or the simulated characteristics in Orbiter are a bit generous, does anyone know which?

Actually both. The Moron-TAL window is calculated with a lot of extra performance left so some damage to the Shuttle remains tolerable.

Also, the Orbiter Shuttle models have all some small and large variations to the real one, especially the default Shuttle.

Finally: The checklist TAL windows are no-communication TAL windows, which means, they have to be very conservative, as the crew has less means to calculate their ability to reach an abort site, than mission control with their radar tracking sites and special computer programs.

 

[Zamzara]

That makes sense, thanks.

 

[Spaced]

I've heard it said that before her accident Challenger was considered the workhorse of the fleet. I've also read that Columbia had more surface tiles and weighed more than the other orbiters. How different was each airframe?
Were there any capability specific reasons for an orbiter's selection for a mission? Or was it simply maintenance and turnaround that specified what shuttle would be available?

 

[GoForPDI]

All the Orbiters had different weights. Columbia was by far the heaviest, she was used mainly for science missions with a pressurised Hab module in the payload bay. All the Orbiters have small differences to each other. I believe either Endeavour or Atlantis (i'm not too sure) was not fitted with plumbing which could attach to the ISS' plumbing, which limited its usable time in Orbit.

 

[Scav]

I believe either Endeavour or Atlantis (i'm not too sure) was not fitted with plumbing which could attach to the ISS' plumbing, which limited its usable time in Orbit.

It was Atlantis, yes.

 

[garyw]

By 'plumbing' do you mean SSPTS?

If so only Endeavour and Discovery had that modification. Atlantis was supposed to be retired first.

 

[MattBaker]

I asked myself how high the Shuttle could fly, so:

A Shuttle with the configuration of 2011, Super Leightweight ET etc, with nothing in the cargo bay.
The orbit should be circular, as an example 600x600.
There should be enough fuel left for an deorbit burn of course.

So, what's possible for the Shuttle? The Hubble missions were, compared to the ISS, missions with a quite high orbit.

 

[Urwumpe]

So, what's possible for the Shuttle? The Hubble missions were, compared to the ISS, missions with a quite high orbit.

Hard maximum is about 700 km circular. That is not only getting at the limits of the propellant resources, but also at the limits of the heat shield.

 

[IronRain]

Not entirely a STS question but it gets close to it.

I was watching the post-flight video of STS-37 and the Gamma Ray Observatory was lifted out of the cargo bay, then one solar panel was deployed, when that was completed the other solar was deployed and then the Hi-gain antenna should have deployed.

Now is my question: Who issues the command to do this? Ground controllers or the shuttle crew? And if it's the shuttle crew do they do it wireless or is there some kind of data transfer possible through the RMS?

Thanks!

 

[Urwumpe]

Not entirely a STS question but it gets close to it.

I was watching the post-flight video of STS-37 and the Gamma Ray Observatory was lifted out of the cargo bay, then one solar panel was deployed, when that was completed the other solar was deployed and then the Hi-gain antenna should have deployed.

Now is my question: Who issues the command to do this? Ground controllers or the shuttle crew? And if it's the shuttle crew do they do it wireless or is there some kind of data transfer possible through the RMS?

Thanks!

Usually, such tasks are done by the Payload Interrogator, an S-band radio system to transmit numeric command codes to a spacecraft.

 

[IronRain]

Was the APAS hatch in the ODS designed to be able to be opened from the outside? If yes, how?

 

[Urwumpe]

Was the APAS hatch in the ODS designed to be able to be opened from the outside? If yes, how?

The ODS is just installed on-top of the external airlock and has no own hatch. You can actually even remove the ODS by EVA, by removing many, many screws.

All three hatches of the external airlock are essentially the same and all have a pressure equalization valve that can be operated from both sides of the hatch, to vent the pressure inside the external airlock. Once the pressure is equalized, you can open the hatch by the same bellcrank mechanism as you use for leaving the Shuttle.

There is no protection for not venting the whole crew cabin atmosphere into space, but the valve does not have such a high volume flow, that you can't just slam the inner door closed if somebody steals your air.

 

[Unstung]

"Q/A's FOR STS" has been merged into "Q/A's about ISS", the former name of this thread. The purpose of this change is for the updated thread to become more inclusive so people can post any spaceflight question here. Hopefully there will be more random spaceflight questions now.

---------- Post added at 11:16 PM ---------- Previous post was at 10:40 PM ----------

I've attempted to answer some astronomy questions on other websites, so in the spirit of this update, I'll post some Q&A that involves spaceflight.


Q: How did the Voyager probes return images before digital camera sensors were commonly used in spacecraft?

A: Voyagers captured and returned images without any CCDs (digital sensors) before the technology became more widely used. The primitive spacecraft used vidicon TV camera tubes, technology that has been around since the 1930s. The tubes could even burn out if pointed at a bright object like the sun.

Data is sent as radio signals via Voyager's high-gain antenna and received by ground stations. The signals might use amplitude (AM) of frequency modulation (FM) to carry information. Software tells the space vehicles to return data to the Deep Space Network. Ground computers are programmed to reconstruct images taken specifically by the Voyagers which have converted information from the analog TV tubes into digital signals.


Q: What makes asteroid Ceres arguably a more interesting target for Dawn than Vesta other than Ceres' greater mass?

A: Ceres was likely to have an underground ocean which froze over time and the ice left over on its surface sublimated due to temperatures being higher in the asteroid belt than the outer solar system (which is cold enough for ice to not sublimate). The ocean was created by heat from radioactive decay from the core early in the dwarf planet's history, but it is possible that there is enough energy left for Ceres to still retain some of its ocean. If water is discovered on Ceres, extra precautions must be taken with the Dawn mission.

Simply put, planetary protection prohibits Dawn from getting too close to Ceres. The possibility of contaminating the world may affect future observations.

 

[Zatnikitelman]

How do spacecraft on-orbit ensure that fuel is fed through the propellant lines? I know there can be an ullage maneuver to move the propellant where it needs to go, and that they pressurize the tanks typically with helium, but how do the ullage thrusters themselves get propellant?

 

[Urwumpe]

How do spacecraft on-orbit ensure that fuel is fed through the propellant lines? I know there can be an ullage maneuver to move the propellant where it needs to go, and that they pressurize the tanks typically with helium, but how do the ullage thrusters themselves get propellant?

There are many solutions for the problem, all called "propellant utilization systems". For example, you can have a metal mesh around the outlet that lets the fuel stick to it by surface tension. Or use a moving shield/piston in the tank (that is done in the Space Shuttle OMS). Or you use a flexible metal membrane between propellant and pressurant gas, that is mostly done by Russian spacecraft.

The bigger the tank, the harder it gets to access all propellant in microgravity.

 

[Capt_hensley]

So simple answer? Yes or No, Hatch controls on both sides of hatches?

 

[Urwumpe]

So simple answer? Yes or No, Hatch controls on both sides of hatches?

Simple answer: Nes

Longer answer: Depends on, what the purpose of the hatch is.

Longer answer II: If you mean the external airlock of the Shuttle: Yes.