TDRS Query

Greg D. Moore (Strider) wrote:
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.

Competing payload requirements can play a factor even if the launch mass
is not excessive.

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.

Right, it makes no difference to the IUS. All the IUS really cares about
is that the line of nodes of the orbit should be aligned with the GSO
target at the time of IUS ignition. That drives launch window but not
altitude.

DI vs. SI makes no difference. In either case, the OMS-2 burn is used to
circularize the orbit on non-rendezvous missions, so the orbit is no
longer elliptical at the time of IUS deploy.

On Apr 15, 8:23 am, "Jorge R. Frank" wrote:

All the IUS really cares about is that the line of
nodes of the orbit should be aligned with the GSO
target at the time of IUS ignition. That drives launch
window but not altitude.

Intuitively though, might not one expect the IUS to successfully reach
its target altitude if its ignition was at a sufficient altitude? Are
you saying that at the time of IUS ignition, there is no lower
altitude limit on the shuttle's circularized orbit?

DI vs. SI makes no difference. In either case, the OMS-2 burn is used to
circularize the orbit on non-rendezvous missions, so the orbit is no
longer elliptical at the time of IUS deploy.

I finally found an explanation of that yesterday, in the press kit for
STS-43. That mission also had an elliptical DOI (circularized to ~160
nm by the OMS-2 burn).

BTW -- in the STS-43 specs below, does "post-Sep 1" refer to TDRS/IUS
sep?

Apogee, Perigee at MECO: 157 x 35 nautical miles
Apogee, Perigee post-OMS 2: 160 x 159 nautical miles
Apogee, Perigee post-Sep 1: 177 x 161 nautical miles

I'm guessing that it does refer to TDRS/IUS sep, and that even with
"DOI," the shuttle reachs its ultimate elliptical orbit only after
TDRS/IUS deploy and an "OMS-3" burn. If I'm guessing correctly, does
"DOI" refer only to the shuttle's intermediate circular orbit?

If not, it appears that even with a "DOI," two OMS burns are required
to reach the shuttle's final orbit. Seems a bit ironic, no?

JTM

On Apr 13, 11:43*pm, Brian Thorn wrote:
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.


From http://spaceflightnow.com/atlas/ac139/000626tdrs.html:

Current status: After years of operation, NASA removed TDRS-1 from
full-time service at its 49 degrees West longitude slot due to its
degraded health. Today the craft provides part-time coverage of the
Antarctic region in support of the National Science Foundation. Its
orbit is currently inclined 10.5 degrees.

Okay, the fact that it has a current status at all makes it better
than I had thought. I do recall that at the time it was launched, they
knew THEN that it was going to be TDRS-spare and replaced by the next
two successful TDRSes because of its problem.

Surely after TDRS-B's fate TDRS-A didn't seem so bad. Certainly not as
bad as it did when it was the lone TDRS flying.

Eric

On Apr 17, 6:17 pm, Eric Chomko wrote:
On Apr 13, 11:43 pm, Brian Thorn wrote:

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.

Fromhttp://spaceflightnow.com/atlas/ac139/000626tdrs.html:

Not Found
The requested URL /atlas/ac139/000626tdrs.html: was not found on this
server.

Current status: After years of operation, NASA removed TDRS-1 from
full-time service at its 49 degrees West longitude slot due to its
degraded health. Today the craft provides part-time coverage of the
Antarctic region in support of the National Science Foundation. Its
orbit is currently inclined 10.5 degrees.

Okay, the fact that it has a current status at all makes it better
than I had thought. I do recall that at the time it was launched, they
knew THEN that it was going to be TDRS-spare and replaced by the next
two successful TDRSes because of its problem.

Surely after TDRS-B's fate TDRS-A didn't seem so bad. Certainly not as
bad as it did when it was the lone TDRS flying.

Andre

On Apr 15, 8:23*am, "Jorge R. Frank" wrote:

DI vs. SI makes no difference. In either case, the OMS-2 burn is used to
circularize the orbit on non-rendezvous missions, so the orbit is no
longer elliptical at the time of IUS deploy.

As I attempted to state in an earlier reply, there seems to be a bit
of confused wording from NASA about this:

http://tinyurl.com/5sadv9 (STS-29)

"The ascent profile for this mission is a direct insertion. Only one
orbital maneuvering system thrusting maneuver, referred to as OMS-2,
is used to achieve insertion into an elliptical orbit. This direct-
insertion profile lofts the ascent trajectory to provide the earliest
opportunity for orbit in the event of a problem with a space shuttle
main engine.

The OMS-I thrusting maneuver after main engine cutoff plus
approximately two minutes is eliminated in this direct insertion
ascent profile. The OMS-I thrusting maneuver is replaced by a 5-foot-
per-second reaction control system maneuver to facilitate the main
propulsion system propellant dump.

Because of the direct-insertion ascent profile, the external tank's
impact area will be in the Pacific Ocean south of Hawaii."

JTM

On Thu, 17 Apr 2008 19:31:03 -0700 (PDT), Andre Lieven
wrote:


Fromhttp://spaceflightnow.com/atlas/ac139/000626tdrs.html:

Not Found
The requested URL /atlas/ac139/000626tdrs.html: was not found on this
server.

Dump the colon ( from the end. Works fine.

http://www.spaceflightnow.com/atlas/...00626tdrs.html


Brian

Well great, you answered your own original question, in which you had no
particular interest in the first place.
---

The OMS-I thrusting maneuver after main engine cutoff plus
approximately two minutes is eliminated in this direct insertion
ascent profile. The OMS-I thrusting maneuver is replaced by a 5-foot-
per-second reaction control system maneuver to facilitate the main
propulsion system propellant dump.

Because of the direct-insertion ascent profile, the external tank's
impact area will be in the Pacific Ocean south of Hawaii."

JTM

** Posted from http://www.teranews.com **

On Apr 20, 3:39*pm, "Revision" wrote:
Well great, you answered your own original question, in which you had no
particular interest in the first place.

I originally asked about Mission 51-L, not STS-29. DOI was not part of
the plan for Mission 51-L, and I was well aware of that.

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.)

NASA says a summary timeline was not available when the STS-6
Press Kit went out to reporters. From the NASA Archives we find:

http://tinyurl.com/4m5k5o

"Orbit Altitude: 184 nautical miles"

That altitude seems too high. Other references give lower altitudes
(some much lower).

Also, I'm a bit surprised that nobody here has mentioned STS-6 having
an insertion orbit that was a good deal less than 175 nm.

JTM