Status Report

Testimony of Larry Knauer, Pratt & Whitney, Given at a Senate Science, Technology, and Space Hearing on Space Propulsion

By SpaceRef Editor
June 3, 2003
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Mr. Chairman, Senator Breaux and other members of the Subcommittee, I am Larry Knauer, President of Pratt & Whitney’s Space Propulsion and Russian Operations in West Palm Beach, Florida. I want to thank you for the opportunity to testify today on the issue of space propulsion.

As you are aware, Pratt & Whitney is a division of United Technologies Corporation. UTC provides high-technology products and services to the aerospace and building systems industries throughout the world. In addition to Pratt & Whitney, UTC’s industry-leading companies are Carrier, Otis, UTC Fuel Cells, Hamilton Sundstrand and Sikorsky.

. Current Investment in Space Propulsion Our estimates of this market, over the last 20 years, indicate that domestic annual sales of in-space propulsion have been less than $150 million per year. Also, industry and government respectively have invested less than $10 million per year, and only a small amount of government funding has been available to industry through contracts. As a result, the non-U.S. space industry has overtaken and in some cases surpassed the United States in the area of in-space propulsion.

Every satellite launched utilizes several types of in-space propulsion and the benefits of improvements are great. The introduction of electric propulsion to satellites could allow over 2000 pounds of extra payload, or years of extra life on station.

Although the potential pay-off for in-space propulsion technology is great, one major reason for low industry investment has been insurance cost, which is typically prohibitively high in the risk-averse space industry. In some cases the insurance premium can be an additional 20% of the total launch cost, if it can be obtained at all. A change in a $1M to $3M propulsion system can add enough risk to raise the insurance premium as much as $20M. Therefore, it is important that new in-space propulsion systems be initially proven on government systems. After the technology has been successfully flight proven, incorporation into commercial systems can proceed with acceptable insurance premiums.

Need for a Robust Space Propulsion Program A robust in-space propulsion technology program will ready the technologies for transition into the commercial marketplace and achieve revolutionary improvements in space exploration capability. As a nation, we will continue our exploration of the solar system, and eventually undertake manned exploration of Mars, when the time and technology are right. During this process, in-space propulsion will mature and transition to the commercial market. NASA has recently reaffirmed the historical reality that propulsion breakthroughs have been and continue to be the basis for revolutionary improvements in exploration capability.

To date, the benefits of electric in-space propulsion have been demonstrated on several spacecraft, but have been limited by the power generated to drive them. The maximum power available has been less than 25 KWe and gives a spacecraft great station keeping weight reduction using ion ìZIPî thrusters. The thrust levels of these systems are so low that station keeping is all they have been able to provide. If you attempted to use one of these systems for final orbit circularization it would take as long as 6 months to get the satellite to its final destination. Recent improvement in Hall effect thrusters, HET’s, have shown the potential to reduce the transfer time to 60 days with 25 KWe power sources. Other technology breakthroughs, which are in development could significantly improve this capability. Raising an orbit some 20,000 miles with today’s on orbit electric propulsion takes months; 40,000,000 miles to our nearest planetary neighbor requires even more efficiency and thrust.

Nuclear electric propulsion, as embodied by project Prometheus, is a bold and courageous step in expanding our exploration capability. Project Prometheus will develop the 100 KWe power system, including the reactor, space radiator system and power electric thrusters needed for small payload delivery to the outer planets. Once on station (not just flying by), the same power system will enable robust and long-term science vastly expanding our knowledge and enabling us to bring the wonders of the solar system back to planet Earth.

Beyond Prometheus, as a nation we should consider continued investment in in-space propulsion to significantly reduce the cost and risk of manned Mars exploration. Small investments toward this end can provide avenues to reduce the cost by 30 to 50%, when we begin this exciting journey. As with Prometheus, these investments will also provide high leverage in-space commercial benefits along the way.

Desired Features of Future Systems Technical features of future in-space propulsion systems include:

High specific impulse (i.e., fuel mileage) reduces the fuel mass of the vehicle departing earth orbit.

  • This reduces requirements for the earth to orbit launcher, therefore reducing launch costs.
  • The lighter earth departure mass is also much easier to accelerate to its final destination.


  • Acceleration depends mostly on thrust and is needed to reduce trip time to distant destinations.
  • Passive propulsion systems, such as solar sails, lack this key feature and are also dependent upon the direction of the ‘solar-wind’ and are therefore limited in their application.

Optimized combination of thrust and specific impulse:

  • Historically, weight growth and cost growth have been problems for new space systems.
  • The initial system weight must be kept low on a percentage basis such that small weight growth, inevitable during development, does not negate the payload capability of the system.
  • The complexity must be minimized to enable reliable deployment and operation of the system.

Challenges for In-Space Propulsion Considering these guidelines, expanding Prometheus capability for manned Mars exploration will provide additional in-space propulsion challenges. Although the power levels needed for the astronauts’ welfare and safety remains at 100 KWe or below, the power levels needed for the electric propulsion system will grow by one or two orders of magnitude, due to the heavier increased payloads. While the scaling of the Prometheus reactor would be relatively straightforward, as demonstrated by our Navy ship and submarine experience, the scaling of the supporting subsystems will present major challenges. Of particular concern are the scaling and space logistics involved in the launching and deployment of the space radiator system. This massive subsystem is needed to reject the excess heat of the electrical power conversion system. Also, scaling of Prometheus will limit the initial reliability to be that of a ënew’ system, as the tried-and-true power conversion systems and electric thrusters must be reinvented in a much larger size.

Additional In-Space Propulsion Ideas/Technologies An alternative to rejecting the excess system heat for the more demanding manned Mars missions would be to convert this ëlost’ energy into direct thermal thrust using a bimodal nuclear propulsion system. A bimodal nuclear propulsion system leverages the best of current propulsion systems in addition to the systems to be matured during project Prometheus. A bimodal nuclear reactor would be configured to provide ~15Klb of direct thermal thrust during earth departure then reduce the power level to the 100 KWe level needed for the astronauts’ welfare and safety during the mission and to support the electric propulsion needs after earth departure. This approach would avoid the need to develop space radiator systems, which are potentially unmanageable. It would also allow the direct use of the 100 KWe power conversion and electric thruster systems that will be flight proven during Prometheus operation.

Bimodal systems were seriously considered to satisfy the nearer term exploration missions, but suffered from a lack of maturity in area of the required reactor fuels. Although fuel solutions exist, based on breakthrough fuel development near the end of the 1960s NERVA nuclear propulsion program, the cost and schedule risks to the Prometheus program were considered to be too high.

In order for a bimodal system to be considered for the Mars exploration mission a relatively low cost fuels development program could be pursued, in parallel with the Prometheus program, to increase its maturity.

Additional in-space propulsion technologies needed for Mars exploration are those that support in-situ propellant utilization. Lewis and Clark would not have completed their mission if they had to carry water for themselves and their propulsion (horses) for the whole trip. They knew water would be available along the way.

Similarly, in-situ propulsion systems for robust space exploration should be aggressively developed. In-situ propulsion systems are designed to use earth-return propellants acquired after reaching the desired destination. This approach avoids the need to carry earth-return-propellants into and then out of earth orbit to the desired destination. Recent strong indications of water on both the moon and Mars elevate this in-situ approach from the category of science fiction to the category of science reality.

Of particular interest is methane/oxygen propulsion technology. Methane (CH4) and oxygen (O2) can be manufactured from the water (H2O) and the carbon dioxide (CO2) atmosphere of Mars. Full utilization of this approach can reduce the required mission mass and therefore the cost by over fifty percent, once again highlighting the high payoff that can be reaped from in-space propulsion improvements.

Conclusion This committee’s interest in in-space propulsion technologies will encourage government and industry cooperation in this field. Government and private sector commitments of investment and resources will accelerate the development of technical advances, while reducing the cost and risk of deployment. Future space explorers will travel on systems developed and funded as a result of decisions made by our government and industry leaders today. Pratt & Whitney is ready to be a part of those decisions and those commitments.

SpaceRef staff editor.