Progress - The Swiss Army Knife of Spacecraft

Shortly after noon today, a Soyuz rocket blasted away from the Baikonur Cosmodrome in Kazakhstan, carrying a cargo vehicle known as "Progress" to the International Space Station. There are a number of spacecraft resupplying the ISS these days* but Progress is (arguably) the most versatile.

In order to operate a space station you need a number of recurring services:

• Delivery and return of crew members
• Delivery of consumables (food, water, oxygen, fuel)
• Delivery of hardware (station parts, spacesuit parts, science experiments)
• Removal of waste (food packaging, broken hardware, completed experiment hardware)
• Orbit and/or attitude adjustments (rotate orientation, increase or decrease altitude to avoid orbital debris or to compensate for atmospheric drag--yep, at 250 miles there's still enough air to slow it down!)

Progress can handle all of those tasks but one; carrying crew to and from orbit. The reason for this lack of capability is that Progress is a direct descendant of the crewed Soyuz spacecraft, which has been the workhorse of Russian spaceflight in constant operation (and upgrade) since 1967, with great successes**. Rather than develop a completely new vehicle, the Russian space program chose to adapt their proven design into a cargo-only vehicle.

The Progress is composed of three segments: a pressurized cargo module, a refueling module, and an instrumentation/propulsion module.

The forward, somewhat spherical segment is the pressurized cargo area that will contain nearly 4,000 lb. of hardware, food, and some water that the cosmonauts and astronauts will manually remove once this portion of the vehicle docks with the ISS. In the months after this cargo is unloaded, that same area will be filled with the multiple forms of waste that life inevitably generates.

At the center of the spacecraft is the refueling module. As you can see in the diagram, this segment is filled with a number of tanks that contain fuel, oxidizer, and sometimes water. Not all missions require more water to be transported so there is some variation in this segment. Again, this segment could hold nearly 4,000 lb. The fuel can be transferred from Progress to ISS by connections in the docking ring, where the two spacecraft meet, eliminating the need for crew to be exposed to hazardous materials. As far as I know, Progress is currently the only spacecraft capable of this function, making it that much more important to station operations.

In the crewed Soyuz this space is the descent module where the crew's seats and instruments are located. To return to Earth, the forward segment and propulsion segment behind it would detach and a heat shield between descent and propulsion modules would protect the crew during atmospheric reentry. No such shielding is needed for Progress. Remember all that trash to be loaded in the cargo area? It's meant to be burned during atmospheric reentry.

The final segment at the rear of the vehicle not only does the work of navigating Progress to the ISS, it also serves as an instrument of orbital adjustment. While the ISS has it's own on-board engines for attitude and orbit adjustment, it is wiser to use those of the visiting spacecraft because the hardware on the ISS must remain on orbit for years (in the end it will be multiple decades) while the visiting spacecraft is newer and more recently inspected to assure safe and effective operations. This also reduces the need to transfer fuel between vehicles. The Space Shuttle was able to facilitate these orbital adjustments but that system was retired in 2011. The Japanese HTV can also provide reboosts but is an infrequent visitor to ISS, leaving the Russian Soyuz and Progress to do much of the work.

So as you can see, Progress really serves as many vehicles. It is the delivery truck, it is the fuel tanker, it is the tow truck, and it is the garbage truck for the International Space Station. It's not glamorous work but it all has to be handled. With all of these support tasks taken care of, the crew can get down to their true purpose on orbit: scientific experiments that, in one way or another, will advance the knowledge and abilities of humanity as a whole. So I suppose you could say that ISS needs Progress to enable progress.

Has there ever been a more appropriately named vehicle?

________________________________________________________________________________

*Current: Progress (Russia), Dragon (USA), Cygnus (USA), H-II Transfer Vehicle (Japan)
  Retired: Space Shuttle (USA), Automated Transfer Vehicle (Europe)
  Future:  Dream Chaser (USA)

**Of course, Soyuz has also had its set of failures. But that's a matter for another time.