Re: Do cargo-hauling astronauts really lift 15 tons?

This is a newsgroup, it's a news. So you, what's your point?

On Thu, 04 Aug 2005 08:48:16 +0800, Captain! <SpammersMustDie@xxxxxxx> wrote:


"zaitsev" <zaitsev@xxxxxxxxxx> wrote in message
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http://msnbc.msn.com/id/8778761/

ANALYSIS
By James Oberg
NBC News space analyst
Special to MSNBC
Updated: 8:33 p.m. ET July 31, 2005



James Oberg
NBC News space analyst
In the weightless environment of space, keeping track of "weight" seems to
be a big challenge for NASA. The most recent example of this difficulty
has to do with the figures on how much useful payload, really, has been
delivered to the international space station by the shuttle Discovery.

Miscounting such materials could contribute to public confusion over what
sorts of future spacecraft need to be developed to replace the space
shuttle fleet when it is retired in 2010. If the shuttle's performance
capabilities are not portrayed accurately, it will be harder to assess the
required attributes for the successors to the shuttle.

In press kits and on NASA Television, the figure "15 tons" keeps popping
up as the amount of supplies being transferred from the shuttle to the
station. Some reports say that's the weight of "items stowed in an
Italian-made cargo unit." After unloading all those supplies, the story
goes, the shuttle will be filled up with an only slightly smaller amount
of garbage: 13 tons.

Does the cargo really weigh that much? First of all, in scientifically
precise terms, there actually is no "weight" in orbit, since all objects
are falling freely through a gravity field that curves their path around
the earth. So any reference to the weight of objects in orbit actually
refers to their mass, which on Earth's surface is typically the same
number.

What's more, a closer examination of NASA documentation reveals that the
actual mass of material being swapped between the shuttle and the station
amounts to only a half to a third of the figures being bandied about. Most
of the "15 tons" refers not to the transferred cargo but to the containers
in which the cargo is transported. Those structures are then refilled and
returned to Earth, not left aboard the station at all.

Counting the containers as payload makes about as much sense as the post
office charging you postage for the weight of the mailbox, or an airline
assigning the weight of your seat to your baggage allowance. It's probably
not a deliberate deception, but the figures do border on the bogus.

If you take stock of all the items that were packed inside Discovery's
Italian-made Raffaello cargo module, you'll find that less than two tons'
worth is actually delivered to the station and left behind. There are
about 2,200 pounds (1,000 kilograms) of transferable cargo and a
1,600-pound (720-kilogram) medical science rack for the station's Destiny
laboratory module.

Precious 'down-cargo'
Once emptied of this material, the Raffaello module will be loaded with
about 5,000 pounds (2,270 kilograms) of "down-cargo," mostly but not
entirely trash. (The trash is not simply tossed overboard because it might
orbit around and recontact the station, damaging it). The down-cargo also
includes some very valuable components destined to be repaired and reused.

Probably the most critical such items are guidance computers for the
Russian spaceships in the manned Soyuz and unmanned Progress series. These
suitcase-sized units are the heart of Russia's "Kurs" ("Course")
rendezvous controllers, and they are mounted in the front of every Russian
ship that docks at the space station. Since that section of the visiting
craft is always jettisoned and incinerated during descent into Earth's
atmosphere, for years the valuable electronics (and other hardware items)
have been routinely removed and stored on the station for return to Earth
aboard shuttle flights.

But the suspension of shuttle visits over the last two and a half years
has meant the gradual accumulation on the station of a backlogged stash of
guidance computers. It got so bad that the spacecraft factory in Moscow is
close to running out of usable units completely, and the return of at
least a few of the stranded computers is desperately needed.

Another piece of returning hardware is also hardly garbage, although it
certainly is broken. This is the malfunctioning control gyroscope, due to
be replaced on the shuttle crew's second spacewalk Monday. A new one is
bolted inside a carrier frame in the shuttle's cargo bay. After it is
installed in place of the broken one, that device will come back to Earth
for diagnosis, repair and eventual reuse.

Miscellaneous cargo

Other items are also being left at the station. Quibbling over precise
values shouldn't divert attention from the tremendous importance of what
has been brought up.

The biggest item is a 6,400-pound (2,900-kilogram) tool caddy to be
mounted on the station's exterior, near the U.S.-built Quest airlock. It
will provide electrical power and data hookups for other spare parts to be
brought up later, ready to be installed as needed in place of future
malfunctioning mechanisms.

About 1,400 pounds (640 kilograms) of loose items were stashed in lockers
in the shuttle's mid-deck, from which they mostly have already been passed
through the tight docking tunnel into the station. Once installed on the
side of the station, Raffaello can open an interconnecting doorway more
than twice as wide as the tunnel, allowing refrigerator-sized units to
pass in and out.

Conveniently, the space shuttle's power system uses fuel cells for
electricity, and the waste product is pure water. That water is being
loaded into collapsible plastic containers and hauled aboard the station.
By the end of the mission, perhaps half a ton of the precious fluid will
have been delivered - and it didn't even count as station-bound payload.

So the total amount of material to be left aboard the station comes to
about 13,000 pounds (5,900 kilograms), an impressive and vital cargo to be
sure. But it's far from the 15 tons often quoted by NASA and news outlets.

Coming back to Earth is about 1,300 pounds of stuff loaded into the empty
lockers on the shuttle's mid-deck, and 5,000 more pounds stashed into the
Raffaello cargo hold, and the 600-pound gyroscope in the payload bay open
frame. That's about 7,000 pounds (3,200 kilograms) in all, predominantly
but by no means exclusively "garbage."

The mass brought up to space, and then brought back to Earth, also
includes the 19,728 pounds (8,967 kilograms) called Raffaello's "cargo
element" - the structure used to hold the up-cargo, and then the
down-cargo. This is the "double-bookkept" 10 tons that the oft-published
figures demand underserved credit for.

Pound-for-pound comparisons
With an accurate estimate for the deliverable cargo, the practical payload
capacity of the space shuttle acting as a freight hauler can then be
compared with alternatives. It turns out to be not very different from a
single flight of the European Space Agency's robot freighter, the
Automated Transfer Vehicle or ATV, whose first mission is slated for the
middle of next year.

The same mass of supplies could be sent up on about two and a half
launchings of Russia's old reliable Progress system, although large cargo
items would need specialized exterior-mounting attach points on the
Progress. At a mission cost in the $40 million range, this suggests that
the cargo delivery of a billion-dollar shuttle flight could be matched by
$100 million worth of Progress missions.

As NASA shops around for shuttle replacement capabilities, it needs to
keep these and other options in mind. And it needs to use authentic
figures for the mass of the desired cargo to be transferred.
© 2005 MSNBC Interactive


okay but what's your point?



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