Commentary | Reinventing Space: Dramatically Reducing Space Mission Cost — Spacecraft Technology
This is the eighth in a series of articles on how to go about dramatically reducing space mission cost while maintaining a high level of mission utility. This article discusses using spacecraft technology to reduce cost. Within this arena, there are a great many approaches that can have a major impact on cost, schedule and performance.
Make More Extensive Use of Microelectronics
Since the opening of the space program, one of the great advances in modern technology is the dramatic rise in the use and capability of microelectronics. Although I haven’t seen it yet, I don’t believe any of us would be all that surprised if the next $10 toy we buy for our children or grandchildren could recite all of Shakespeare’s plays in six languages and in response to verbal and sensory clues in the world around it. Making extensive use of this technology for spacecraft offers enormous advantages — systems that are smaller, lighter-weight, lower-cost and exceptionally powerful and versatile.
And yet traditional space programs have been very slow to take advantage of this enormous capability. This is in part because of a perceived need to fly only components that flew on our grandfathers’ spacecraft and in part because of real technical issues such as thermal problems or the need for radiation hardening in some orbits. The thermal and mechanical problems are pretty straightforward to solve. Among the methods to solve the radiation problem are inherently rad-hard materials, radiation protection for these small microelectronic components, and natural radiation protection by burying radiation-sensitive components deep in the spacecraft or behind batteries or propellant tanks. These examples also show another great advantage to small, relatively short-lived spacecraft: We need the components to live for a much shorter period of time and, more importantly, we can take advantage of the rapid advance in technology that is going on all around us.
Use More Cubesat Technology
One of the places where microelectronics technology is being adopted for space use is in cubesats, originally invented in 1999 by Bob Twiggs at Stanford University and Jordi Puig-Suari at California Polytechnic State University. Always dramatically lower cost than traditional space systems, cubesats have become more sophisticated and more competent over time, and because they are flying relatively often, many more components are being qualified by on-orbit experience. Cubesat technology is advancing rapidly, at least coming close to keeping up with advances in modern microelectronics.
An example of this rapid advancement is our own experience on a government program that has been making use of cubesat solar arrays. In the two weeks between when we began preparing inputs for a design review and the time of the review, the price of the commercial cubesat solar arrays had gone down by 10 percent and the performance had gone up by 25 percent. This type of change is unlikely to occur in more traditional programs.
Another advantage of cubesat technology is that most of it is available off the shelf and can be delivered rapidly, such that these components never become part of the critical path. This reduces schedule, allows much more rapid system testing, and means that we don’t have to buy expensive spares, because replacement units are available with the next FedEx delivery.
Make More Extensive Use of Software
One of the most important advances in spacecraft technology is to have the spacecraft do more of the functions in software and less in hardware. This has multiple advantages, such as:
- Lower mass.
- Lower recurring cost.
- Much higher functionality.
- Can be changed, upgraded and fixed on orbit.
It also has some disadvantages:
- High nonrecurring development cost.
- Difficulty managing the development process.
- Difficulty controlling subsystem interfaces that are all in the spacecraft computer.
The ability to fix the software on orbit is a key consideration for reducing cost and increasing reliability. This implies the need to ensure that mission operations have procedures and processes in place to change out the on-orbit software. Doing more in software also implies that there is a major advantage to being able to fly the latest computer available. In effect, the spacecraft becomes a general-purpose processor with most of the work being done in software. Because both software and on-board processors are evolving very rapidly, this reinforces the advantage of lower-cost, short-lived spacecraft. It is likely that you have much more processing capability in your smartphone than many traditional on-orbit spacecraft. This means that newer spacecraft will typically be more competent than older spacecraft, such that the value of an on-orbit asset continues to decline.
Some of the features that we can reasonably expect from future software-controlled spacecraft include:
- Software-defined radio.
- On-board preprocessing of images such that only the needed information is sent to the ground (which also reduces the needed communications bandwidth).
- More responsive systems, such that the spacecraft can send more detailed data if and when they are requested by the end user.
- Autonomous on-board control of both orbit and attitude such that the spacecraft always knows where it is and where it’s looking.
- Precise control of spacecraft motion based on dynamic models such that all motions are both rapid and nearly jitter-free.
These features don’t reduce cost directly, but rather allow low-cost small spacecraft to be much more capable, such that they can do the same job as older, larger, much more expensive systems.
Use Standardized or Commercial Components
In the past, standardization has been remarkably unsuccessful in space technology. This is largely because of the desire to optimize every component for each mission, i.e., “use the standard component, just delete these features we don’t need and add these other features.” However, the use of exceptionally capable processors may make standardization more acceptable in future missions.
One of the most important elements of standardization is the use of more plug-and-play electronics. Here the goal is to make an interface among the various spacecraft components and subsystems that will be essentially similar to the USB port on your computer in which multiple different items can be plugged in and begin to function immediately. This greatly reduces the time and cost associated with spacecraft integration and test. In addition, it allows the potential, for example, of a new more capable or more relevant payload to be put into a spacecraft that is in storage waiting for a need to be launched. We have become very used to this capability in our portable computers and cellphones, such that the very strong advantages are becoming increasingly clear.
Avoid Large Engines
We need very large rockets and rocket engines to get off the surface of the Earth, but once we are in space, they are no longer needed and often do far more harm than good. In the six-hour trip to geostationary orbit, it really doesn’t matter whether our engine burns for 10 seconds or 10 minutes, but the engine that does the job in 10 seconds is a lot heavier, requires an entirely separate control system and typically has more fatal failure modes than very small engines. An example of this is the Clementine spacecraft that successfully orbited the Moon in 1994 and was next heading for rendezvous with an asteroid. The large engine intended to do this job was ignited and Clementine was never heard from again. Small engines may be able to overcome some potential failure modes by, for example, having more than a single engine, and the pointing may be able to be controlled by the existing spacecraft control system.
Use Hosted Payloads
A relatively new approach to reducing spacecraft cost is the use of hosted payloads, in which a secondary payload is added to another spacecraft, such as a commercial communications spacecraft. This is a good example of cooperation in which both sides can reduce cost. The hosted payload can obtain all of the spacecraft bus services at a fraction of the cost of building an entire spacecraft, and the host bus can reduce cost by generating income from selling bus space and services to the hosted payload. Although it wasn’t called a hosted payload, this type of arrangement was used in the original GPS constellation in which the satellites also included a Nuclear Detection System payload. More recently, the U.S. Air Force’s Commercially Hosted Infrared Payload was successfully launched on-2.
Particularly when combined with some of the systems engineering approaches we have previously discussed, spacecraft technology approaches can dramatically reduce mission cost and schedule and allow us to make use of much more modern, lower cost and far more capable technology.
The ninth article in this series will look at government or customer approaches for reducing cost.
James R. Wertz is president of Microcosm Inc. He is co-author of “Reducing Space Mission Cost,” published in 1996, and has been teaching a graduate course at the University of Southern California on that topic since then. If you have questions, comments or suggestions, or simply want to discuss these issues, he can be reached at firstname.lastname@example.org. Information on the joint Microcosm/USC Reinventing Space Project can be found at www.smad.com/reinventingspace.html.