Expendable Vehicles In The U.S. Space Fleet

Some Notes

The Delta IV Heavy

The most powerful expendable U.S. rocket is now the Delta IV Heavy, which lifted off on its maiden flight in December, 2004. The flight was successful but also marked by an anomaly leading to the discovery of a minor design flaw which caused fuel cavitation in a transfer fixture which in turn had resulted in false sensor readings. The flaw has since been repaired and the vehicle is ready for operational use.

The Delta IV Heavy is significantly more powerful than the Atlas V 551, the most advanced and heaviest configuration of the Atlas launchers. The Delta IV Heavy in advanced configurations is estimated to be potentially capable of launching 48,000 pounds into low Earth orbit (LEO), which approximates the capacity of the Shuttle.

With evolution, Boeing^1, the manufacturer, estimates that the Delta IV Heavy could eventually lift a payload of 100,000 pounds into LEO.

The Atlas V

The Atlas V is scheduled to boost the Mars Reconnaissance Orbiter (MRO) into space at 7:55 a.m. tomorrow (Wednesday)^2. The Atlas V launching the MRO will use the 401 configuration (one common core booster and one Centaur upper stage, no solids).

The MRO is significantly larger than any other Mars orbiter.

Comparison

Interestingly, Boeing has just dedicated a West Coast launch site for the Delta IV (including the Medium and Heavy configurations). The Delta IV-H first stage consists of three liquid-fueled RS-68 engines, manufactured in the United States, developing a total thrust of around 2 million pounds. (Each R-68 engine develops more than 600,000 pounds of thrust.)

The RS-68 engine, built by Boeing's Rocketdyne^3, is the first large engine developed in the United States since the Space Shuttle main engine (SSME). The SSME develops a thrust of 350,000 pounds.

The advantage that the Delta IV has over the Atlas V (made by Lockheed Martin) is that the Atlas imports its main engine from Russia.

The Shuttle follow-on will be a combination of vehicles, ranging from Delta IV and Atlas V variants to the Magnum Saturn V-class booster (not described here). Congress may decide to eliminate either the Delta IV or the Atlas V to avoid duplication. If this happens, I hope Congress chooses to preserve the Delta IV.

Next Scheduled Flights

The next flight of the Atlas V is as noted above. The next flight of the Delta IV is scheduled for August 30 and it will be in its Medium configuration. The Delta IV-H will lift off for its first paying customer (the Air Force) in October of this year, carrying a classified payload.

Project Constellation's New Ships

The roster of spacecraft and launchers proposed under the President's Project Constellation as contemplated by NASA's new Administrator, Dr. Michael Griffin, does not involve either the Delta IV-H or the Atlas V for the Crew Exploration Vehicle (CEV) or for use as a heavy lift vehicle. Rather, the Magnum booster may be developed instead as a heavy lift launcher and a modified Shuttle solid rocket booster may be used for the CEV.

Footnotes:

1. Boeing has sold its Rocketdyne unit to United Technologies, effective August 2, 2005. Source: Boeing.com. -- Edited August 10, 2005.

2. The launch was delayed for approximately 48 hours. -- Edited August 12, 2005.

3. See Footnote 1. -- Edited August 10, 2005.

Sources consulted: Boeing website for the Delta IV; Space.com; SpaceNews.com; SpaceRef.com; Howstuffworks.com; and others.

Last updated: August 10, 2005.