Pierre
from Omaha
How long does it take to assemble a Delta II on the pad
and how many people are involved in the process? |
| Well Pierre,
to assemble a Delta II on the pad it takes approximately
six weeks or 45 days. The Delta II Heavy, which this is
the second time we’ve flown this, takes a little
bit longer than that. But we were able to shave eight
days off of the optimum Delta II schedule even with a
more difficult launch vehicle to put up. This was a challenge
that the Opt Agency gave us after the two MER missions
and trying to get SIRTF up this quarter. So we got there
right on the mark and we’re dealing with things
such as weather in the Indian Ocean. So answering your
question, 37 days is the record up to this point for the
Delta II Heavy.
Host: Could you share with us briefly some examples
of what you did to shave that time?
Guest: We worked weekends; that’s how we got there.
Usually we take Saturdays and Sundays off and this time
we worked Saturdays. We also learned a lot from doing
the first Heavy vehicle and were able to shave some
time off of that and get some efficiency. |
RichO
from Elk Grove, IL
If I remember correctly the Delta II Heavy was first used
on the MER-B launch a couple months ago. What did you
learn from that launch that you have improved on this
launch vehicle? How has going to a Heavy launch vehicle
improved the launch process? |
| Rich O,
what we’ve learned is just process improvement.
There’s really nothing that we can go from one vehicle
to the next in this close proximity to improve the vehicle
in this short of time. So what we have donefor the efficiencies
have been in the processing time. It’s not the first
time we’re going through it anymore, and that’s
where we’re getting the most efficiency. And then
the other part of the question you say, how is going to
the Heavy launch vehicle improved the launch process?
It really hasn’t, it’s actually a little more
difficult. What the Heavy does is it widens the Delta
II fleet and allows us to get into bigger payloads or
hotter trajectories or getting out to the distant planets
more readily with more weight; so it expands our fleet. |
Peter
from Basel Swiss
How Heavy is the Telescope? |
| The
telescope is 851 kilograms Peter, and that is the total
spacecraft weight. So I wasn’t able to give you
the actual telescope weight, but the whole complete package
is 851 kilograms.
Host: Is this typically about the weight of a payload
for that size of a vehicle?
Guest: This is a very light payload. We’re used
to hauling a lot more mass than this, but this is a
very large payload. So the trade was made in being able
to get a hot performing vehicle like the Heavy, and
mating that to a light satellite like this which is
very large. The telescope is very high in comparison
to some of the other missions we normally run on a Delta.
So that’s some of the differences.
|
Lenora
from Lakeland , FL
Does the weight of the cargo determine the window you
use to carry the payload into space? If not just how do
you determine the window? |
| Usually
what we try to do is hit a point in space, an imaginary
point in space, where the telescope is going to be able
to do its best science. And weight has a little bit to
do with it, but it’s really the vehicle performance
and getting there. Some vehicles have the added flexibility
of having variable azimuths, in other words they’re
able to change the direction in which they are flying
almost instantaneously throughout a set time period. The
Delta II does not have a variable azimuth; you can pick
one or two at most for every attempt. So I don’t
know if I answered the question completely, but those
are some of the pieces and it’s not just the weight
variable. |
Andy
from Grangeville
What do you feel is the most difficult part of vehicle
processing? Where could the most issues occur? |
|
The most issues can occur at L-4 and beyond. That’s
when the launch vehicle becomes its most active. We
load the RP1 kerosene onboard the first stage. We load
the cryogenic locks onboard. We also start pressuring
the second stage. So things become very active in that
time period. We’re also dealing during that time
with the guidance system, the range assets, and the
weather. So it all becomes very exciting in those last
four hours with all those things interchanging and having
to work correctly to get us off on time.
|
Jerry
from Shrewsbury
Do you anticipate any issues with the cork this time as
you had with the MER-B mission? |
| Absolutely
not, we already went through our locks loading a couple
of weeks ago and we had no deterioration of the cork
bond. So the SIRTF booster is pristine and ready to
go.
Host: For those viewers who are not familiar with the
cork issues; can you just give us a real brief summary?
Guest: Sure, what we had is, we’ve got this cork
around the center body of the Delta II rocket and the
original booster that was slated for SIRTF which we
flew on MER-B, had been sitting out in the elements
for a while. And some water, rain induced and also thermally
induced when we load the locks onboard had gotten behind
this cork and expanded some of it and actually caused
a disbond of the cork to the booster. And so we went
through a lot of iterations trying to get some more
cork bonded to the MER-B booster and suffered some setbacks
in the way that the bond was setting for us. We were
finally able to get that off, and in early July we were
able to launch MER-B. This one is not going to suffer
from that because we’ve added some leak holes
to the area to make sure that any water that’s
behind there will drain properly and the adhesive that’s
on there is the original adhesive that should hold very
well for this application.
|
Juan
Rodriguez from Gijon, Spain
Do you have to take special safety precautions to prevent
problems with the SIRTF liquid helium tank during this
launch? |
| Juan, there’s
safety precautions that are taken while we’re loading
the helium onboard the spacecraft, and that is to protect
the personnel and obviously the spacecraft from suffering
any damage. And helium in itself is not very dangerous,
it’s not explosive, but in the cryogenic condition
it can currently cause some burning if folks are exposed
to it or if it increases rapidly it can asphyxiate some
folks if they’re in a confined space. So all that
is taken before the launch countdown ever takes place.
So we disconnect at L-12 hours and at that point the helium
system is really locked up and there are no other special
safety precautions to take other than the ones we would
use around a fully loaded vehicle. |
Juan
Rodriguez from Gijon, Spain
I have read that you had to reschedule the launch of SIRTF
because you are using a tracking and instrumentation ship
in the Indian Ocean to support launch. Why don´t
you use tracking and data relay satellites? |
|
That’s a great question Juan, and I’ll
tell in the back of our minds we have been developing
a transmitter to use on the Delta’s and the smaller
Pegasus launch vehicle. Unfortunately developing it
and implementing it takes quite some time. What we run
into is SIRTF will be approximately 90 nautical miles
in altitude during this second stage phase, which we
were going to be able to recover data from this ship
in the Indian Ocean. So it takes very low power to get
the signal down from the spacecraft, or from the second
stage down to the ground. It’s only 90 miles so
we’re able to catch it very easily with a telemetry
ship, or ground base type systems, or even an airplane
if we had one available. But if you go to a tracking
and data relay satellite you've got to remember that
these satellites are up at geosynchronous orbit, so
you need high power and you need to be pointing your
antenna in the opposite direction out into space in
the geosynchronous. So when you go to high power you
need higher weight and so you have to make your satellite
smaller or your intended science takes a hit in mass
and you have to take up some additional batteries and
you have to be able to reject heat, which means you
need to have some radiators or heat sicks. So you take
quite a bit of hit if we were to have these types of
transmitters, but we’re headed that way. We’re
trying to make them smaller and miniaturize some of
the components and hopefully we’ll get there in
a couple of years.
|
