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  [Discuss] SpaceX CRS-5 space station mission

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Author Topic:   [Discuss] SpaceX CRS-5 space station mission
Robert Pearlman
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Posts: 31239
From: Houston, TX
Registered: Nov 1999

posted 12-17-2014 05:23 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Please use this topic to discuss CRS-5 (SpX-5), the fifth of SpaceX's 12 contracted Dragon cargo flights to the International Space Station under NASA's Commercial Resupply Services (CRS) Program.

Robert Pearlman
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Posts: 31239
From: Houston, TX
Registered: Nov 1999

posted 12-17-2014 05:28 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
SpaceX has been targeting its CRS-5 launch for 1:20 p.m. EST (1820 GMT) on Friday (Dec. 19).

However, a failed attempt at performing a static fire test on Tuesday (Dec. 16) has led to a possible delay, as late as January. Waiting on word from either (or both) SpaceX and/or NASA...

Robert Pearlman
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Posts: 31239
From: Houston, TX
Registered: Nov 1999

posted 12-18-2014 07:13 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
SpaceX release
SpaceX CRS-5 launch rescheduled for January

While the recent static fire test accomplished nearly all of our goals, the test did not run the full duration. The data suggests we could push forward without a second attempt, but out of an abundance of caution, we are opting to execute a second static fire test prior to launch.

Given the extra time needed for data review and testing, coupled with the limited launch date availability due to the holidays and other restrictions, our earliest launch opportunity is now Jan. 6 with Jan. 7 as a backup.

The ISS orbits through a high beta angle period a few times a year. This is where the angle between the ISS orbital plane and the sun is high, resulting in the ISS being in almost constant sunlight for a 10 day period. During this time, there are thermal and operational constraints that prohibit Dragon from being allowed to berth with the ISS. This high beta period runs from Dec. 28, 2014 to Jan. 7, 2015. Note that for a launch on Jan. 6, Dragon berths on Jan. 8.

Both Falcon 9 and Dragon remain in good health, and our teams are looking forward to launch just after the New Year.

A launch on Jan. 6 would be at 6:18 a.m. EST (1118 GMT), an hour before sunrise.

Headshot
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Posts: 410
From: Streamwood, IL USA
Registered: Feb 2012

posted 12-18-2014 07:20 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
...there are thermal and operational constraints that prohibit Dragon from being allowed to berth with the ISS.
Does anyone know exactly what these constraints are? Do they arise solely from the ISS or Dragon, or a combination of both? This is the first time I have heard of this.

Robert Pearlman
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From: Houston, TX
Registered: Nov 1999

posted 12-18-2014 07:28 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
These beta angle cutouts affect all visiting vehicles (even the space shuttle when it was flying). From a 2002 NASA reply:
The beta angle is the angle between the orbital plane and a line drawn from the Sun to the Earth. As the beta angle increases, the ISS is exposed to more sunlight per orbit, and eventually it will be in constant sunlight — in other words, there is no passing into the Earth's shadow for extended periods of time. This can create thermal problems, so special attitudes are chosen to counter these effects.

The [visiting vehicle] also has thermal constraints under these conditions. Since the attitude requirements of the ISS and [vehicle] would conflict when docked, [visting vehicle]/ISS flights are scheduled to avoid periods when the beta angle exceeds 60 degrees.

Headshot
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From: Streamwood, IL USA
Registered: Feb 2012

posted 12-18-2014 09:39 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
If there are times when the ISS and other vehicles are in constant sunlight, then there should, theoretically, be times when they are also in constant darkness. Does that cause power issues as both rely on solar-generated electricity for power? Also, what about prolonged cold-soaking?

issman1
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From: UK
Registered: Apr 2005

posted 12-18-2014 10:15 AM     Click Here to See the Profile for issman1     Edit/Delete Message   Reply w/Quote
Does this latest problem with a Falcon 9 affect plans for SpaceX to launch the Deep Space Climate Observatory (otherwise known as GoreSat) for NASA and the U.S. Air Force in January 2015?

I truly wish them well with the first stage landing test during CRS-5 but feel they're struggling to match their own expectations.

Robert Pearlman
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Posts: 31239
From: Houston, TX
Registered: Nov 1999

posted 12-18-2014 11:02 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
For now, the launch of DSCOVR remains set for Jan. 23. If SpaceX is successful in launching CRS-5 on Jan. 6, then that would result in a 17-day turnaround between launches. Earlier this year, SpaceX achieved a 14-day turnaround and the company said then that they expected to be able to reduce that time even more.
quote:
Originally posted by Headshot:
...then there should, theoretically, be times when they are also in constant darkness.
There is never a period when the ISS is absent sunlight for part of its orbit. A commenter on the Bad Astronomy blog provided a good way to understand this:
Imagine the earth with its shadow (umbra) cone projecting behind it, away from the sun. The shadow moves up and down 24 degrees with the season due to the tilt of the earth's axis.

Now take a hula hoop which represents the orbit. You can rotate it up and down (inclination) and around the earth's axis (right ascension of the ascending node, RAAN, if you must know). Under some rotations the entire hoop is outside of the umbra cone.

However, it is impossible for the entire hoop to be INSIDE of the umbra cone, which is what is required for a period of constant night.

According to my handy SMAD book (Space Mission Analysis and Design) the longest eclipse (night) period for a satellite at space station altitude is a little over 36 minutes. This is regardless of inclination or RAAN. This happens when the orbit (hula hoop) crosses right through the middle of the umbra cone.

SpaceAngel
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Posts: 156
From: Maryland
Registered: May 2010

posted 12-18-2014 02:22 PM     Click Here to See the Profile for SpaceAngel   Click Here to Email SpaceAngel     Edit/Delete Message   Reply w/Quote
I wonder if they are making sure that the launch vehicle won't have another mishap just like what happened to the Antares/Cygnus in October.

All times are CT (US)

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