TDRS Query

TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.

JTM

wrote in message
...
TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.


I'd look at launch mass and see if there's a significant difference there.


For a geosynch orbital insertin, 175 nm vs. 150 nm probably isn't that much
of a difference, but for a "1st stage" it can be.


JTM

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Greg Moore
SQL Server DBA Consulting Remote and Onsite available!
Email: sql (at) greenms.com http://www.greenms.com/sqlserver.html

On Apr 13, 3:11*pm, "
wrote:
TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.


As I recall TDRS-A was released and immediately had problems. It never
achieved the desired orbit and was of marginal use at best.

TDRS'es are made up of three components, a TDRS-east, TDRS-west and
TDRS-spare. Those plus the ground system make up TDRSS.

TDRS-A eventually became TDRS-spare after the successes of TDRS-C and
D. (Note you use the number designations of which letters were
actually used -i.e. TDRS-1 is TDRS-A, TDRS-2 is TDRS-B, and so on.). I
have lost count where we are right now.

TDRSes orbits, being geo-stationary, are or should be as circular as
possible. They should float above the earth and orbit at exactly 23hr
56min 4sec per revolution (1 day). Lastly, they tend to jiggle in sort
of a figure-8 over their prime spots and occasional burns are needed
to keep them in true geosynchronous position.

On Sun, 13 Apr 2008 20:44:14 -0400, "Greg D. Moore \(Strider\)"
wrote:


TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.


I'd look at launch mass and see if there's a significant difference there.


For a geosynch orbital insertin, 175 nm vs. 150 nm probably isn't that much
of a difference, but for a "1st stage" it can be.

I see M*xs*n is still busily trying to convince the bystanders that he
has a clue.

Don't forget that 51L also carried Spartan-Halley. 51L was
significantly heavier than STS-6 or STS-26.

There's your difference.

Brian

On Sun, 13 Apr 2008 18:17:49 -0700 (PDT), Eric Chomko
wrote:


As I recall TDRS-A was released and immediately had problems. It never
achieved the desired orbit and was of marginal use at best.

Your recollection is faulty. TDRS-A had an IUS malfunction, but was
nurse-maided to its operational orbit via onboard thrusters in time to
support STS-9/Spacelab 1 seven months later. It was eventually
replaced by the later TDRS's and started getting other duties, such as
relay support for Antarctica research stations.

Brian

Brian Thorn wrote:
On Sun, 13 Apr 2008 20:44:14 -0400, "Greg D. Moore \(Strider\)"
wrote:



TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.


I'd look at launch mass and see if there's a significant difference there.


For a geosynch orbital insertin, 175 nm vs. 150 nm probably isn't that much
of a difference, but for a "1st stage" it can be.


I see M*xs*n is still busily trying to convince the bystanders that he
has a clue.


Don't worry...OM is recuperating as we speak (write?) and shall soon
return...his doctors have suggested a sea cruise to get him back in the
true, and he has accepted their sage advice:
http://www.harpers.org/media/image/b.../mobydick2.jpg
"Are you with me, men?" :-)

Pat

On Apr 13, 10:37*pm, Brian Thorn wrote:

Don't forget that 51L also carried Spartan-Halley. 51L was
significantly heavier than STS-6 or STS-26.

I didn't forget that at all.

There's your difference.

That thought entered my mind, but I didn't expect even so much as semi-
official confirmation of it. Taken alone, it seemed almost *too*
dumbed-down. It also seemed too obviously impractical, if not risky.

Are you saying that for 51-L, NASA (or its TDRS contractor) fully
expected to rely even more on the STS-6 emergency procedure? (That
would be consistent with many of the conditions under which Mission 51-
L was launched.)

Jorge usually has an informed opinion on such matters, but maybe this
one is considered too "sensitive" under the circumstances.

JTM

On Apr 13, 8:17*pm, Eric Chomko wrote:
On Apr 13, 3:11*pm, "
wrote:

TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.

As I recall TDRS-A was released and immediately had problems. It never
achieved the desired orbit and was of marginal use at best.

Thanks Eric. We're getting old, lol, but I too recall that TDRS-A was
of marginal use.

TDRS'es are made up of three components, a TDRS-east, TDRS-west and
TDRS-spare. Those plus the ground system make up TDRSS.

TDRS-A eventually became TDRS-spare after the successes of TDRS-C and
D. (Note you use the number designations of which letters were
actually used -i.e. TDRS-1 is TDRS-A, TDRS-2 is TDRS-B, and so on.). I
have lost count where we are right now.

In some references to TDRS, NASA uses numerical designations:

http://tinyurl.com/5roel5

This NASA page shows where we are now:

http://tinyurl.com/6e5me3

Here's a non-NASA link:

http://216.92.110.5/atlas/ac144/021201tdrss.html

TDRSes orbits, being geo-stationary, are or should be as circular as
possible. They should float above the earth and orbit at exactly 23hr
56min 4sec per revolution (1 day). Lastly, they tend to jiggle in sort
of a figure-8 over their prime spots and occasional burns are needed
to keep them in true geosynchronous position.

STS-26 was a Direct Orbital Insertion (OMS-2 burn only, elliptical),

STS-6 (with two OMS burns, as planned for 51-L) was launched well
prior to the first DOI (41-C). I don't recall offhand if the STS-6
insertion orbit was circular or elliptical. (I'm looking for more
details on that, as well as STS-29.)

JTM

On Apr 14, 10:20*am, "
wrote:

STS-6 (with two OMS burns, as planned for 51-L) was launched well
prior to the first DOI (41-C). I don't recall offhand if the STS-6
insertion orbit was circular or elliptical. (I'm looking for more
details on that, as well as STS-29.)

http://science.ksc.nasa.gov/shuttle/...on-sts-29.html

The NASA page linked to above simply says "Altitude: 184 nm." Just as
curtly, however, the STS-129 press kit says "Altitude: 160 nm." A NASA
page I found yesterday gave an insertion orbit for STS-29 of around
175 nm. There must be a reasonable explanation for at least some of
this, but what is it?

JTM

On Apr 13, 2:11*pm, "
wrote:
TDRS-1, TDRS-3, and TDRS-4 were all released from orbiters that had
insertion orbits in the neighborhood of 175 nm. (I'm not sure if all
of those were elliptical.)

Okay, I can now provide additional NASA links if required. Only the
latter two orbiters had elliptical insertion orbits. Both were Direct
Orbital Insertions (DOI).

TDRS-2, however, was to be released from Challenger after Mission 51-L
had reached a circular insertion orbit of about 150 nm.

STS-6 also had a circular insertion orbit; but like the one planned
for Mission 51-L, it was not a DOI.

Orbital mechanics is not my strongest suit, At any rate, I'm looking
for a dumbed-down explanation of the apparently unique insertion orbit
planned for Mission 51-L's release of TDRS-2.

In other words, why was the 51-L insertion orbit so much lower than
the ones for STS-6; STS-26, and STS-29; and why did NASA switch to
elliptical DOI for STS-26 and STS-29?

JTM