Question General Spaceflight Q&A

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Oh okay. I think I've got it now. Thanks for answering, I'd always wondered that, since in pictures you don't really get an idea of which way it's headed.
 

Orbinaut Pete

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This is the "normal" attitude for the ISS:


This is the attitude the ISS flies in while the Shuttle is docked:
 

Donamy

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That's alittle misleading Pete, that second one should read "Docked Attitude".
 

Urwumpe

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Also, the reasoning is wrong, as the exospheric drag depends only the the whole cross-section and not just the frontal area. You would need to draw the shuttle and the ISS from the front to see the difference. And the docked altitude is also wrong. Even during TEA, the shuttle is at the front. The Shuttle is at the aft during the reboost attitude.
 

tblaxland

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And the docked altitude is also wrong. Even during TEA, the shuttle is at the front. The Shuttle is at the aft during the reboost attitude.
During STS-119 they were flying with the Shuttle at the aft to give it additional MMOD protection, even when not doing a reboost. I remember because they had to rotate it around to the front to provide additional drag as a type of debris collision avoidance manoeuvre. (I just checked the flight plan and it confirms the "BIAS -XLV -ZVV" attitude, STS-124 too)

EDIT: There are different TEAs: US forward, Russian forward, even "sideways", ie, truss along velocity vector - I saw a study of their stability somewhere.
 

Urwumpe

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Strange, my lecture notes still have the TEA with USOS forward.
 

DaveS

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tblaxland: That's the standard docked attitude since STS-114. Before STS-114 they flew with the underbody into the VV. After Columbia, they realized how fragile the TPS is so they decided to flip the entire stack around so that the leeside of the orbiter now faces the VC.
 

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Hey guys, i saw a video of the crew of a shuttle mission testing the snares on the RMS, how exactly does that hold onto to objects large enough as Hubble or something, they only look like bits of wire.
Thanks.
Ryan.
 

tblaxland

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Hey guys, i saw a video of the crew of a shuttle mission testing the snares on the RMS, how exactly does that hold onto to objects large enough as Hubble or something, they only look like bits of wire.
Thanks.
Ryan.
By moving slowly. From this page, I estimate the end effector acceleration at 0.01 '/s/s for a 32,000 lb payload. This equates to a force of 43 N, or about the force required to pick up a largish baby.
 
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Urwumpe

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Additionally, you have to differ between snaring and rigidizing. The first just closes the wires, so the object is loosely connected to the RMS, the rigidizing retracts the wires and pulls the grapple fixture into the RMS end effector, so it is tightly connected to the RMS. Tightly connected in this case means: A force of 4000N pulling the grapple fixture against the end effector.
 

Orbinaut Pete

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The RMS latches onto a grapple fixture on the payload.
There are two types of grapple fixture:

FRGF (Flight Releasable Grapple Fixture).

The FRGF is the standard grapple fixture that is used on all Space Shuttle payloads.

PDGF (Power & Data Grapple Fixture)

The PDGF is used on the ISS. It provides power to the Space Station RMS, so that the SSRMS can be operated from many different locations on the ISS.


The way grappling actually works, is as follows.
The RMS uses its camera and the alignment aid target that you can see at the top of the FRGF image above, to loosely align itself with the grapple fixture.
The silver probe you see sticking out of the FRGF is called the grapple pin. This is what the RMS actually latches on to. When the grapple pin is inside the end of the RMS (called the Latching End Effector, or LEE), the 3 LEE snares are fired. Firing the snares centres the grapple pin inside the LEE, and also forms a tight grip on the grapple pin by the LEE (see illustration below).

Rigidization pulls the entire grapple fixture tight against the LEE, so that the grey coloured base plate you see on the FRGF is flush against the LEE.
As you can see on the grapple fixture images above, there is a small, white "cap" on the top of the grapple pin, which stops the pin from slipping out of the snares when the payload is rigidized (see link at bottom of post for graphical description).
The gold coloured "fingers" that you see on the grapple fixture are called ramps. On the end of those ramps, you can see silver bits. These are called roll cams. Roll cams help guide the LEE itself into an exact alignment with the grapple fixture during rigidization, and also ensure that the LEE stays firmly in place during RMS movements.

As you can see from image #1 of the LEE below, the LEE has 3 spaces cut away around its edge, where the roll cams slot into place. You can also see the snares once they have been fired, and in the very end shot and image #2, you can see the tight grip that the snares form around the grapple pin.
#1

#2


Below is also a diagram of the payload grappling sequence, which explains all of the above graphically:
http://iss.jaxa.jp/iss/3a/orb_rms2_e.html
 
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ryan

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Socks

Has anybody been watching footage from the ISS and noticed that all the astronauts have socks on, is this for comfort reason or just becuase the amount of materials around they dont want to hard the material or the astronaut. I've noticed this in some Shuttle footage too.
Thanks.
Ryan.
 

tblaxland

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Has anybody been watching footage from the ISS and noticed that all the astronauts have socks on, is this for comfort reason or just becuase the amount of materials around they dont want to hard the material or the astronaut. I've noticed this in some Shuttle footage too.
Can you think of any advantages of wearing boots? I see no advantages, so why fly them given the extra mass they would take? Or were you thinking barefoot? If so, personally, I think my feet would get cold, especially with no gravity to pull the blood down there.
 

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Not only that but it would be uncomfortable.
 

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[FONT=Verdana,Geneva,Arial,Helvetica,sans-serif][SIZE=-1]>After the docking, the station was reoriented as planned to minimize the risk of micrometeoroid/debris impacts upon the Shuttle (-XVV = -x-axis in velocity vector, +z-axis in local vertical)[/SIZE][/FONT]

Can someone explaine how to do this???
 

tblaxland

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[FONT=Verdana,Geneva,Arial,Helvetica,sans-serif][SIZE=-1][/SIZE][/FONT]Can someone explaine how to do this???
In Orbiter? I would use Attitude MFD. Switch to Velocity mode and set a Pitch of 180°. Depending on which version of the ISS you are using you will also need to set a Roll of either 90° or 180°.
 

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What's the weight/volume limit for personal effects? Could I take a Les Paul and a small amplifier up with me?
 

Urwumpe

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What's the weight/volume limit for personal effects? Could I take a Les Paul and a small amplifier up with me?
No, each would be too heavy - also you should remember that there is not unlimited electrical power on the ISS. I remember Thomas Reiter was allowed to take only pictures in digital form and replacement strings for an acoustic guitar with him, that is a good maximum reference - the acoustic guitar is "standard equipment" on the ISS.

I don't know the exact mass limits, but you are only allowed to take very few personal things with you.
 
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