RE: STS-131 Entry View Opportunities Over US April 19 morning local time

tom.m.erkenswick@nasa.gov

Jim Oberg posted this explanation on the FPSpace list (cross-posted with permission):

From: fpspace-bounces@friends-partners.org [mailto:fpspace-bounces@friends-partners.org] On Behalf Of James Oberg
Sent: Monday, April 19, 2010 8:16 AM
To: Charles, John B. (JSC-SA211); fpspace@friends-partners.org
Subject: Re: [FPSPACE] Why is it rare? [Rare Shuttle Re-entry over theContinental USA]

Some upper atmospheric clouds -- 'noctilucent' clouds' -- apparently
are a potential threat in summer months.

Descending node also tends to cross populated areas, especially at the
range-to-touchdown on the same order as Columbia debris impact.

Descending node landing occurs about 4 revs after ascending node, as a
rule. That's six hours. This can also be useful for crew timeline planning.

Recall that orbital precession is about 6 deg/day for 52 degrees,
which makes landing opportunities about 24 minutes earlier every day.
For a 15 day mission, that's 6 hours earlier than launch time. This requires
crew sleep shift -- or switch to descending node.

For crew sleep shifts matched to existing space station crews, the
option was usually not exploited since the crew had to shift earlier
anyway, either for moscow time (Mir) or ISS (GMT).

We designed the orbital inclinations (otherwise a 'free variable')
for some Spacelab missions so as to 'tune' this effect so that by using
a descending node landing profile, the orbit would precess just right so
that with the descending node landing, the mission duration was
close to an even day -- so little if any crew shift was required.

For example, STS-78, Life and Micrograv Spacelab, was at 39 degrees
so as to make mission duration 16 days 22 hours. STS-73 (USML 2) in
1995 was at 39 degrees so as to make mission duration 15 d 22 hr.

-----Original Message-----
From: seesat-l-bounces+tom.m.erkenswick=nasa.gov@satobs.org [mailto:seesat-l-bounces+tom.m.erkenswick=nasa.gov@satobs.org] On Behalf Of Patrick Schmeer
Sent: Tuesday, April 20, 2010 8:22 AM
To: SeeSat-L@satobs.org
Subject: Re: STS-131 Entry View Opportunities Over US April 19 morning local time

STS-131 landed 13 minutes ago.

Why had such a landing track across the USA been chosen?
In order to avoid a night landing at KSC?

Patrick

--- djlaszlo@aol.com <djlaszlo@aol.com> wrote:
> -----Original Message-----
> From: SpaceWeather.com <swlist@spaceweather.com>
> To: SpaceWeather.com <swlist@spaceweather.com>
> Sent: Sun, Apr 18, 2010 9:53 am
> Subject: Rare Shuttle Re-entry over the Continental USA
> 
> Space Weather News for April 18, 2010
> http://spaceweather.com
> 
> SPACE SHUTTLE RE-ENTRY:  On Monday morning, April
> 19th, space shuttle Discovery will make a rare
> "descending node" reentry over the continental United 
> States.

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