A few decades ago, space propulsion was defined by either chemical thrusters or cold gas thrusters with very few exceptions. In recent years, ion thrusters have been shown to be a viable and enabling propulsion technology, and as a result have breathed life into other ideas such as solar-sail propulsion or micro-propulsion, with regards to feasibility.
The problem that has developed with new types of space propulsion though is that each successive implementation pushes the bar higher in terms of performance and with this, expected risk mitigation. At the same time mission schedules are being made tighter and launch dates pencilled in sooner, which will ultimately result in an impossible situation in which cutting-edge performance is being asked of the satellite and subsystems, almost in an instant.
Something clearly has to change in the way newer types, and even existing types of space propulsion, are developed and used on space missions. This article suggests 3 alternative approaches and reasons on how to improve the design and implementation of missions involving newer space propulsion devices. Each suggestion is offered such that the end goal of achievable flight heritage for the propulsion system, at a realistic cost, is met.
Suggestion 1 — Simplify the performance requirements of the propulsion unit to only 10 requirements or less
Due to the enormous risk associated with getting any type of satellite or probe into space (currently 1 in 12 to 13 missions have a failure according to Flight International) it seems paradoxical that the propulsion system has to frequently meet a myriad of technical and product assurance requirements to mitigate risk.
The real problem with this thinking is that is severely underestimates the time and effort taken to achieve technical verification of requirements. The second and possibly more important issue is that having lots and lots of requirements does not mean that the most critical requirements are recognised and given priority.
A better, though radical, approach is to drastically and forcibly reduce the amount of requirements on the propulsion system. Having 10 or less requirements would be a good number. This allows more chance of meeting deliveries and of getting tangible and repeatable successes in testing and verification stages.
Suggestion 2 — Address at all times what the customer really wants
In psychology, marketing and advertising it has long been common knowledge that human beings have and act on basic needs. In the early twentieth century, Abraham Maslow even specified these needs into a hierarchical structure. All actions that we take are driven by some kind of need and usually when one of these needs is not being met, then irrationality and obsessive behaviour often results.
How many space projects, or even any engineering project, have you been involved in where less critical requirements seemed to take centre stage and waste lots of time in being addressed?
The reason behind this is that if the basic needs of your customer are not being addressed then at a psychological level they will look for certainty in any place.
It is also important to note that the requirements specification is not what the customer actually wants in their head; it is an abstraction, a map, that is created to fulfill the convention of contracts and engineering requirement documents.
The job, then, of you the supplier is to constantly ask and engage with the customer to have them articulate, person to person, their ideal images of what a successful propulsion system looks like. It is important to do this even if the customers do not build or have expertise in propulsion. For example, they may have worked on a previous mission and there was another propulsion system that performed in a certain way. What they would actually like is that your system had a lot of the elements of that system, or as close as you can achieve with your technology, but with some extra functions.
As per convention, though, they had to translate that design configuration into a specification. The specification is not, however, the picture or the working model in the head of the customer.
In addition, it is also important to do this within your project team and company. By addressing these needs and by acknowledging these ideal images, you focus on what the customer and what people inside your team want and can act appropriately and responsibly for the project without being side-tracked.
You may notice how Suggestions 1 and 2 are interdependent.
Suggestion 3 — Test more, plan less
Following directly on from Suggestion 2, if the needs of the customer are being met then you will build a sense of “us together” rather than “them and us”. This is especially useful when it comes to testing and verifying requirements or just building up confidence at the unit qualification stage.
The key objective is to spend much less time in meetings trying to make a test procedure or test plan perfect and acceptable, and spend much more time testing the hardware and making it work!
When you test you get that valuable property of a tangible result. The data that you obtain can then be used to further development or to demonstrate that you meet requirements there and then. It is best to plan only for more testing and to arrange your documentation such that it represents the minimum of obstacles in the path from thinking about a test to implementing the test.
Though this seems like an obvious suggestion on paper, in practice in depends on how your relationship develops with the customer and how you have stripped away all but the critical requirements for the propulsion system.
The fact of the matter is that everything should be tested and tested again if possible before it goes into space. This idea of testing and testing again is actually a motto in the marketing industry as without testing money and effort is wasted and your campaign is much less effective in producing the desired outcome: sales.
These 3 suggestions, I believe, are crucial if any new space propulsion system is to be given a chance of flying. The simpler the system the quicker it can be built and tested, delivered and flown. Developing new technologies for space is not the time for every wistful dream and want to be realised; it is the time for only the most simple and crystallised ideas to be turned into reality.
It is also important to remember that for commercial companies no mission can fly if it is not cost-effective. The trend is still to use next-generation space propulsion as “loss leaders” but this actually means perpetuating the practice of trying to meet too many requirements in too short a time.
Satellite missions can be made to be cheaper, simpler and more importantly be delivered on time if strong principles of simplification and focus are adhered to.
For a good example: the delivery of the first Galileo satellite (GIOVE-A) by Surrey Satellite Technology Ltd was realised by only focusing on a handful of critical requirements for a large part of the project. In doing this the satellite was delivered for launch on time and as can be seen from the results, did its job adequately.
Another huge obstacle is re-educating engineers, managers and scientists to see the benefits of a radically simple approach. There is perceived safety in lots of requirements and boxes to tick, but this perception is artificial.
A frank summary would be this: It does not matter how fancy or well-documented your propulsion system is, if it has not flown yet then it is next to useless!
This should always be born in mind when thinking about space propulsion project design and specification.