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


"zaitsev" <zaitsev@xxxxxxxxxx> wrote in message
news:op.suwwenk4yhe8wr@xxxxxxxxxxxxx
>
> 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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