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Author
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Topic: Shuttle v. SS-1
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spaceuk
Member Posts: 2113
From: Staffs, UK
Registered: Aug 2002
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posted 06-27-2006 12:13 PM
  
Interesting comparison noting that SS-1 reached max altitude of 69.59 miles during X-prize run and this Saturday's Shuttle will achieve zero gravity point at about 68.9 mile altitude.
Phill
spaceuk
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Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 06-27-2006 12:20 PM
Maybe I am over thinking this, but Phil can you explain the source for this figure (68.9 miles)? Strictly speaking, there is no "zero gravity point" — zero gravity, or microgravity, is not a location, its a factor of acceleration. STS-121's orbital insertion is 122 nautical miles (140 statute miles or 225.94 kilometers). So where or how does the 68.9 mile (statute or nautical) factor? [This message has been edited by Robert Pearlman (edited June 27, 2006).] |
spaceuk
Member Posts: 2113
From: Staffs, UK
Registered: Aug 2002
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posted 06-27-2006 12:39 PM
I thought is was just one of those interesting close-prox figures to 'focus-on' the tremendous achievement of SS-1 flights when judged against shuttle figures.SS1 reached 367,442 feet (69.59 mile)[S/F Now) while the "zero gravity" point for shuttle should be reached at 68.9 mile (S/F Now ascent data file]. Please don't lose any sleep over this one! I'm more concerned over the Camarda incident and the shuttle-launch sign-off overrides by seniorKSC launch personnel than these close-prox figures! Phill
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Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 06-27-2006 01:06 PM
Sorry Phil, I didn't realize MECO was so low. I had always assumed (given the altitude of their orbit) that the orbiter would be well past 70 miles at 8 minutes and 31 seconds into flight. But you're correct and it is an interesting coincidence... thanks.[This message has been edited by Robert Pearlman (edited June 27, 2006).] |
MCroft04
Member Posts: 1634
From: Smithfield, Me, USA
Registered: Mar 2005
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posted 06-28-2006 07:14 PM
I'm still wondering how the shuttle reaches the 122 mile orbit, with a MECO and "weightlessness" at about 70 miles. To get to the 122 mile orbit from MECO at 70 miles the shuttle has to travel another 52 miles in elevation before reaching the 122 mile orbit. Wouldn't this have to be at constant velocity (no acceleration) if the astronauts are in a "weightless" state? Clearly I'm not knowledgable in the science of getting into orbit (or "on" orbit as the astronauts say), so perhaps someone can explain the details. |
Ben
Member Posts: 1896
From: Cape Canaveral, FL
Registered: May 2000
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posted 06-28-2006 07:45 PM
When MECO occurs they are in a highly elliptical orbit that 'coasts' up to the apogee on the opposite side of earth. It is here, about 42 mins after launch, when they fire the OMS engines to circularize the orbit at the higher altitude (about 200 miles for ISS).As an example, on unmanned launches the same maneuver is known as an 'apogee kick burn.' Launches into geosynchronous orbit only require the rocket to take it into an upward coasting 'transfer' orbit. At the top of the coast (think of a parabola...like throwing a fly ball), which is 22,000 miles, before it begins to fall back towards earth, the apogee kick motor fires an pushes the satellite into that high orbit at 22,000 mi. The basis behind it is using the least amount of fuel to achieve a desired ortbit. [This message has been edited by Ben (edited June 28, 2006).] |
LT Scott Schneeweis
unregistered
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posted 06-28-2006 08:47 PM
It is basically a Hohmann transfer ...------------------
Scott Schneeweis
URL http://www.SPACEAHOLIC.com/ [This message has been edited by LT Scott Schneeweis (edited June 28, 2006).] |
MCroft04
Member Posts: 1634
From: Smithfield, Me, USA
Registered: Mar 2005
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posted 06-29-2006 11:45 AM
Thanks for the good explanations. I hadn't considered the elliptical orbit. |
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