Surviving the Launch and Operating in Space
Part 1 in a Series of articles about Why Getting in Space Takes so Long (And Is so Expensive)
By Dr. Diego Casadei, Head of Space R&D at Cosylab
“Rocket science”, apart from being a well-defined engineering sector in astronautics, is also an idiomatic expression indicating something overly complex, detailed or confusing. Well, Wikipedia [1] also tells us that it is the title of several musical and entertainment shows … and “it’s not rocket science” is a way of telling somebody that you don’t think that something is particularly difficult to do or understand.
I work on space instrumentation since the late nineties and I still find this field very stimulating, thanks to the many technical challenges, which are often addressed with brilliantly simple solutions. But I tend to agree that the actual discipline has much in common with the idiomatic meaning of “rocket science”. In the first lab where I worked, at the INFN Bologna, where we developed the time of flight system of the Alpha Magnetic Spectrometer [2], we attached a panel with a modified version of Young’s Handy Guide to the Modern Sciences [3]:
If it is green or it wiggles, it is Biology.
If it stinks, it is Chemistry.
If it doesn’t work, it is Physics.
If it doesn’t work and costs billions, it is Space Science.
You can guess which was our addition.
The biggest issue in space science
After two successful space missions (AMS-01, operated on the NASA shuttle Discovery in June 1998, and AMS-02, installed on the International Space Station in May 2011 and still in operation), one instrument already delivered to ESA and waiting for the flight (STIX on board of ESA Solar Orbiter, to be launched in 2020), and one instrument under development (MiSolFA), I got convinced that the biggest issue in space science is the couple of contrasting requirements that
(1) the new mission should bring orders of magnitude improvements to have any chance of being selected and
(2) one should only use known-to-work (i.e. obsolete) systems in space.
As it is usually impossible to achieve breakthroughs using old technology, the solution is to develop and “qualify” new systems, designed to satisfy demanding requirements in terms of limited mass, volume, power consumption and dissipation, electromagnetic noise and susceptibility, and telemetry. When talking about “space qualification” we usually mean a quite precise process, to make sure that the equipment is capable of withstanding the severe conditions during the rocket launch (strong vibrations, venting due to quick depressurization, and shocks in correspondence of detaching segments) and the harsh conditions during operation (vacuum, big thermal excursions, high radiation).
Let’s consider one particular example, the thermal range. For a given orbit and desired satellite attitude (in the sense of orientation [4]), the Sun will illuminate it with an incidence angle, which in general changes with time. Satellites in low-Earth orbits (say 400–800 km above the sea level) typically enter the Earth shadow once per orbit (i.e. typically once every 1.5 hours or so), which makes a big difference in terms of absorbed power. Thus, a simulation is carried on to estimate the temperature at different points of the spacecraft, taking into account the emission from the Sun and the power dissipated by each device, and the resulting temperatures are plotted as a function of the time. As the initial simulations do not contain very realistic satellite configurations, conservative assumptions are made about the local heating and the heat flow from hot to cold regions (and eventually irradiated to space).
Next, different orbits and attitude changes are accounted for, obtaining an envelope which should almost certainly contain the actual conditions. The maximum and minimum temperatures with operative and non-operative equipment are then recorded as the expected mission range (“non-op” temperatures enclose the operational range, of course). The uncertainty on the simulation is quantified and is then added in the most conservative way, i.e. by subtracting it from the minimum temperatures (non-operative and operative) and by adding it to the maximum temperatures (operative and non-operative). This is taken as the “acceptance range” for the Flight Model (FM) of the instrument (or satellite), which must be tested against these limits before being accepted for the integration on the satellite (or rocket). However, the “qualification range” is wider than this “acceptance range”: additional margins are applied (in the most conservative way) and the “Qualification Model” (QM) should be tested successfully within the qualification range. The QM is identical to the FM, but it gets overstressed by the qualification tests, hence it’s preferable not to send it to space. In short, the FM must pass all tests at acceptable levels, but only after the QM was shown to be successful at qualification levels (hence it is preferred to build the FM after the QM, to have a chance to make changes, in case qualification tests go not so well). Similar procedures are applied for vibration testing, and for electromagnetic compatibility.
Vibration tests of MiSolFA components:
Now you can understand why space projects take so long (typically 10–15 years from proposal to space) and are so expensive. On the other hand, they are very reliable: the number of failures in space is remarkably low, considering the high complexity of the development process (spanning years with heterogeneous groups with high turnover) and the extreme conditions to which the systems are subject.
TO BE CONTINUED…
In Part 1, you have seen what it takes to demonstrate that the equipment is most likely to be able to survive the launch and operate in space. In Part 2, Diego shares more about how this is achieved and what are the keys to success.
Don’t miss the next story!
About the author
Diego Casadei has a Ph.D. in Physics and long experience in space instrumentation. He worked on two cosmic-ray detectors, AMS-01 (flown on board the NASA shuttle Discovery in 1998) and AMS-02 (installed on the International Space Station in 2011), and two X-ray telescopes, STIX (on board ESA Solar Orbiter mission, to be launched in 2020) and MiSolFA (a very compact instrument under development). His contributions range from detector R&D to the design of trigger and data acquisition systems, from instrument characterization to space qualification, from simulations to performance studies. He managed tasks of increasing complexity, with recent roles of technical coordinator for STIX and project coordinator for MiSolFA. Currently, he is the Head of Space R&D at Cosylab.
Article References
[1] https://en.wikipedia.org/wiki/Rocket_science
[2] http://ams02.org/
[3] http://health.uottawa.ca/biomech/laws/science.htm but see also https://en.wikipedia.org/wiki/Murphy’s_law and Murphy (https://en.wikipedia.org/wiki/Edward_A._Murphy_Jr.) who was an aerospace engineer who worked on safety-critical systems
A good reference is also http://murphyslaws.net/ of course.
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