ATV-2 Johannes Kepler

Keeping the International Space Station (ISS) supplied will become an increasing challenge with the retirement of the US Space Shuttle in 2011. This is the first in a series to look at how the ISS will be serviced for the next five or six years.

The Japanese were schedule to launch their second H-II Transfer Vehicle (HTV-2) resupply mission today, 20 January, but weather has caused the mission to be rescheduled for a possible launch on Saturday.

The Russians fly their Progress spacecraft on resupply missions, and the next one is scheduled for 28 January.

Johannes Kepler ATV-2
ATV-2 Johannes Kepler
Image Credit:
European Space Agency (ESA)

The European Space Agency (ESA) has flown their Automated Transfer Vehicle (ATV-1 or Jules Verne) to the ISS once before on 9 March 2008, and their next launch is coming up on 15 February 2011.

On the commercial side, Space X has successfully orbited their Dragon spacecraft and returned to Earth. Their next test flight is penciled in for July and the first resupply mission is penciled in for December.

And Orbital Sciences Corporation has their first cargo delivery test of its Cygnus spacecraft scheduled for December 2011.

That summarizes the partners working to support the International Space Station.

Here is a more detailed look at the European Space Agency’s ATV system.

The 20 ton Johannes Kepler ATV has a cargo capacity of up to 7 metric tons. The composition of this load can vary depending on the mission:

  • 1.5 to 5.5 metric tons of freight and supplies (food, research instruments, tools, etc.)
  • up to 840 kilograms of drinking water
  • up to 100 kilograms of gases (air, oxygen and nitrogen)
  • up to four metric tons of fuel for orbit correction and up to 860 kilograms of propellant to refuel the space station.

The spacecraft is compose of two main sections. The first is the ATV Service Module (below, left), which is not pressurized, includes propulsion systems, electrical power, computers, communications and most of the avionics. The ATV uses four main engines and 28 small thrusters to control the navigation of the spacecraft. Four solar panels are deployed after launch and supply 4800 Watts of power to the batteries and the electrical systems.

The second component is the Integrated Cargo Carrier (below, right). The large section in the front is pressurized and comprises about 90% of the cargo volume. It handles all the dry cargo, including the racks on each side. The inhabitants of the International Space Station access this area through the hatch in the Russian docking system.

Service Module
ATV Service Module & Four Main Engines
Image Credit: ESA

Service Module
Cutaway of ATV Cargo Carrier
Image Credit: ESA

The Equipped External Bay of the Integrated Cargo Carrier (ICC) holds 22 spherical tanks of different sizes and colors (below, left). These tanks are used to re-supply the Station with propellant for the International Space Station propulsion system, various gases (air, oxygen, and nitrogen) and water for the crew.

The contents of these tanks are delivered to the Station through dedicated connections, or through manually operated hoses.

Service Module
ATV Liquid Resupply Tanks
Image Credit: ESA

Docking Module
Russian Docking Module
Image Credit: ESA

The ATV uses the Russian-made docking equipment sensors to perform the approach and docking sequence (above, right). The procedure is the same as with the Soyuz manned capsules and the Progress resupply spacecraft.

The Russian docking system enables physical, electrical and propellant connections with the Station. Access to the ICC is through the Russian hatch.

Once the ATV is securely docked, the crew can enter the cargo section and remove the payload, which usually includes maintenance supplies, science hardware, parcels of fresh food, mail and family tapes or DVDs.

Pintle Injector Rocket Engines

by Dave Fischer

We have had several queries concerning “pintle injectors” (make sure you read the last paragraph of this post), as these are mentioned in the Space-X page on the Falcon 9, where it refers to the Merlin rocket engine and the “pintle style injector“:

The main engine, called Merlin 1C, was developed internally at Space-X, drawing upon a long heritage of space proven engines. The pintle style injector at the heart of Merlin 1C was first used in the Apollo Moon program for the Lunar Excursion Module (LEM) landing engine, one of the most critical phases of the mission.

Based on the queries and the Space-X information, we went sleuthing. First, we came across the fact that TRW built the LEM descent engine, which used the pintle injector. We ran across David Meerman Scott’s blog apolloartifacts for a discussion and look at a model of the famous Lunar Module Descent Engine (LMDE). The engine was made famous by the Apollo 13 mission, where:

the Service Propulsion System (SPS) was never used subsequent to the cryotank stir/explosion. Because the extent of damage to the SPS was unknown, there was great concern at the time that collateral damage could have caused a catastrophic malfunction (if the engine was fired). Instead the LMDE was used for the return burn and subsequent course correction. Quite a famous engine.

In 2000, TRW demonstrated the TR-106 engine (pintle injector) using LOX / LH2 at NASA’s John C. Stennis Space Center . The engine generated 650,000 pounds of thrust, more than the 400,000 pounds of thrust generated by the Space Shuttle Main Engine SSME. Al Frew, vice president and general manager, TRW Space & Technology Division stated:

Most engines are designed for maximum performance and minimum weight, but we deliberately set out to develop an engine that minimizes cost while retaining excellent performance. We believe this engine will cost 50 to 75 percent less than comparable liquid hydrogen boosters. By reducing engine costs, which make up almost half of the cost of a launch vehicle, we will reduce the cost of launch vehicles and access to space for government and commercial customers.

Despite the promise the motor demonstrated, NASA canceled further work.

The pintle injector engines have a long history in the former Soviet Union. The NK-33 was the successor to the NK-15 engines used in the failed Soviet N1 Moon launcher. NK-33 have been used with the Russian Proton launch system. An interesting discussion of the Soviet Moon rocket, its engines and the NK-33 successor can be found here, along with spectacular video of the launch and explosion. Orbital Sciences has now contracted with Aerojet (owner of the NK-33 engines) to finish developing and testing the NK-33 engines, now designated as AJ26-58 for the Taurus II.

Jonathon Goff, at Masten Space Systems, had a commentary at Selenianboondocks on the 2006 Space-X change from an ablative Merlin engine to a regenerative engine. Jon states that the “engine related problems are interrelated, and that they have to do with the combination of using a high chamber pressure engine design with a pintle-injector and an ablatively cooled chamber wall.” That is, the flame produced by the cone of fuel and oxidizer hits the wall of the chamber and overheats the wall.

Included in the commentary is a simplified image of a pintle injector rocket engine, which illustrates the flow of liquid oxygen and fuel (RP-1 or liquid hydrogen) through the pintle injector into a cone shaped spray in the combustion chamber.

The replacement of the ablative chamber with a regenerative chamber eliminates the overheating.

Pintle Injector
Pintle Injector
Image Credit: Forschungsgruppe Alternative Raumfahrtkonzepte

Below left is the business end of the LEM Descent engine, showing the Pintle Injector:

Below right is an image by Warren W. Thompson at the unveiling of Space-X’s Falcon 1 at the Air & Space Museum on 4 December 2003.

Lunar Module Descent Engine
Image Credit: jurvetson on Flickr
Merlin Engine with Pintle Injector
Merlin Engine with Pintle Injector
Image Credit: Warren W. Thompson

Finally, while explaining the Pintle Injector to a friend, I realized that almost everybody who has a garden or tends a lawn has personal experience with pintles. You all use a nozzle on the end of your watering hose. Crank it down and you get a steady, narrow stream of water shooting out in a long arc. Crank it back the other way when you want to shut it off, and you get a wide, cone shaped fan spray. Now, turn off the water and look at the business end of the garden hose nozzle (please shut the water off first). There in the middle is a round pintle that moves back and forth as you crank the outer casing one way or the other. And the fan shaped spray of water with which you are familiar is what the fuel and oxidizer spray looks like inside the rocket engine. So take another look at the two images above and imagine the fan shaped spray. The only difference is that your spray of water doesn’t explosively combust and throw a rocket into space.