[FWD] Congress tells NASA not to give up on manned Hubble service mission

JOE HECHT wrote:
So you are saying a .3km/s over many days will not get you that far.
Am I understanding this right?

No, it can achieve all of .3 km/s total. There's a difference between
acceleration and velocity. The problem is if you planned a burn to last
an entire day, and at the end of the day you wanted to be going .3 km/s
faster, at the end of that day you'd be out of fuel. Your margin of .3
km/s would be used up. If you had enough fuel to achieve a speed
increase of .3 km/s every day then yes, of course you could do it.

(Please don't top post.)

--
bp
Proud Member of the Human O-Ring Society Since 2003

Jorge R. Frank wrote...
So you are saying a .3km/s over many days will not
get you that far. Am I understanding this right?

0.3 km/s won't get you there no matter how many days
you spread it over.

(To summarise)
I think Joe is asking whetner a 0.3 nudge will allow the orbit to drift
into the desired plane over time. It won't.

The orbital plane is the orbit's angle to the equator. A nudge will change
it by so many degrees, but it will stay at that plane until it is given
another nudge. To change the plane by x degrees requires y amount of delta
v. There is no significant drift.

- Peter

In article ,
Jorge R. Frank wrote:
Are there things on the shuttle that could be taken off to reduce
other weight to make burn more effective?

No.

More accurately: yes, but not enough to make a substantial difference.

The shuttle doesn't carry a lot of unnecessary mass. Yes, there are some
things that could come out, if you were willing to accept some degree of
inconvenience. It's been done once or twice; STS-36, in particular,
reportedly was a severely bare-bones flight, because it took a heavy
military payload into an orbit slightly beyond the shuttle's normal
limits. But we're talking differences of at most a few percent there.
Such measures aren't going to turn 0.3 into 0.4, never mind 3+.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Yes,

Thats the question properly translated by someone who knew what I ment.

If I push .3 left ( or cross plane or to change plan) what stops me from
drifting left before I get where I want so long as i keep my RCF to
myself( off)


"Peter Smith" wrote in message
...
Jorge R. Frank wrote...
So you are saying a .3km/s over many days will not
get you that far. Am I understanding this right?

0.3 km/s won't get you there no matter how many days
you spread it over.

(To summarise)
I think Joe is asking whetner a 0.3 nudge will allow the orbit to drift
into the desired plane over time. It won't.

The orbital plane is the orbit's angle to the equator. A nudge will
change
it by so many degrees, but it will stay at that plane until it is given
another nudge. To change the plane by x degrees requires y amount of
delta
v. There is no significant drift.

- Peter

JOE HECHT wrote...
Yes,

Thats the question properly translated by someone who
knew what I ment.

If I push .3 left ( or cross plane or to change plan)
what stops me from drifting left before I get where I
want so long as i keep my RCF to myself( off)

What stops you is that you don't just want to get to a particualr position.
What you want to do is get to a particualr position travelling at a
particular speed and going in a particular direction. All these conditions
must be satisfied for you to be able to dock the shuttle to the ISS (the
original scenario IIRC).

So you need a particular vector. To do that, you need to add your current
vector to a vector produced by your rocket (RCS). If that rocket vector is
not big enough, you will not get the required result. Waiting around
drifting changes your position, not the vector.

- Peter

"JOE HECHT" wrote in message
ink.net...
Yes,

Thats the question properly translated by someone who knew what I ment.

If I push .3 left ( or cross plane or to change plan) what stops me from
drifting left before I get where I want so long as i keep my RCF to
myself( off)

There is no "drifting". Think of it this way. Imagine a hockey puck
traveling in a certain direction. You apply a force perpendicular to the
direction of travel for a short time (hit it with a hockey stick). This
alters the direction vector of the hockey puck, but only when the force is
being applied. Once that force is removed, the puck continues to move in a
straight line.

When changing orbits, the same thing applies. Once the force is removed,
the orbit stays the same. The exceptions are only for other outside forces
like molecular drag (in LEO), solar wind, and the like.

The only way you can "catch up" to another object in orbit is by entering
the same orbit as the object you're trying to catch. When you're talking
about plane changes, there are few "tricks" that can save fuel.

Assuming you're in LEO and the plane change is really great, you can change
your orbit to a highly elliptical one with a very high apogee, do the plane
change at apogee, then circularize back into a LEO orbit. This can save you
some fuel compared to doing the plane change in LEO, but it is still going
to be very expensive in terms of fuel. Furthermore, such a maneuver makes
you travel through the van Allen radiation belts, which aren't very good for
electronics, particularly things like solar cells.

Jeff
--
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