In my blog last month, Why All This Stringent Testing?, we took a look at a few reasons why a stringent set of testing is performed on components going into space applications. The existence of radiation and the issue of extreme temperature variations are straightforward. It is commonly taught in science class that the Earthís atmosphere does a pretty good job of protecting us here on Earth from harmful radiation that exists in space. It does not keep out everything by any means, but it is a great protective barrier. On top of that our skin does a pretty good job as well with the remaining low energy particles. Obviously, it is not impermeable either since we as humans can have some rather adverse effects if exposed to an unsafe level of radiation. In addition to radiation concerns and large temperature variation there are other factors to consider for space applications as well. One of these factors is the mission life for the application. Mission life requirements impact several other design criteria which we will get to shortly.
Designs for space applications are commonly created with mission life expectations reaching 15 to 20 years and even longer in some cases. The lifetimes in commercial communications are much shorter with designs being replaced in as little as 5 years and sometimes even less than that. The fast-paced market of commercial communications sees design cycles with annual, perhaps even bi-annual, releases in some cases. By contrast, design cycles are in many cases 3 to 5 years in space applications. This is quite different than communications designs that are being launched constantly to keep up with increasing demands for more data and throughput. Designing for space applications takes longer because there are so many factors to consider for qualification and assurance that the design will last for the expected lifetime. Also, there is no feasible option for replacement once a design is deployed into space.
In the last 10-12 years the communications industry has gone from 2G data rates, in the 700 kbps range, up to the LTE data rates of today in the 20-30 Mbps range. In just a little over 10 years there has not only been this increase in data rates but about four different ďgenerationsĒ of communications equipment to enable each incremental step from 2G up through LTE. As we speak there is a lot of buzz surrounding the next generation of 5G equipment which looks to push data rates into the Gbps range. By contrast, in approximately double the time period that the migration from 2G to LTE occurred, the Cassini orbiter was launched and then spiraled into Saturn. In 1997 the Cassini orbiter launched, reported back an incredible amount of data over its lifetime, and then performed its death spiral into Saturn in 2017. That is a whopping 20-year mission life! The 20 years of mission lifetime does not include the design, qualification, and test phases completed before the orbiter was even launched. Iíve included a graph with examples of various NASA missions launched over the last 25-30 years to give some perspective on the long lifetimes required for space applications.
Mission Life Times for Various Space Applications
As you can see from the graph, the majority of missions shown have lifetimes of at least 10 years. For example, the Hubble Space Telescope was launched in 1990 and is still being used today. That is a remarkable 28 years that it has been in service. The International Space Station was launched in 1998 and is still in use as well, albeit with retrofits along the way. Some have shorter mission lifetimes such as the Parker Solar Probe which was just recently launched and is expected to operate until around 2025. There are many more we could discuss which would take much longer than that in the limited space we have here on this blog. What I have included here should give a good sampling of the typical mission lifetimes. You can see more about these different missions in the links at the end of this blog.
In order to enable mission lifetimes, such as those show here, it is important to have reliable components in a robust design. Designers must weigh out factors such as cost, power, weight, and size. All of these parameters must be considered and prioritized depending on the particular application.
Even in designs for space, where total system cost is quite high, there is still pressure on the overall cost of the project. As with any design the desire is to make a good return on investment which means that design engineers and component engineers need to be smart when selecting components to ensure the design needs are met and cost goals are achieved simultaneously.
Power is an important parameter to consider as well since the application requires long lifetimes on battery power. This is of particular importance when the mission takes the design further from the sun where it is harder to recharge batteries from solar energy.
Weight is of concern for a couple of reasons. The heavier a design weighs, the more expensive it is to launch it. In addition, there is guidance and steering considerations to make sure the design stays on its proper trajectory during its lifetimes. The heavier a design is, the more fuel it takes to fire the thrusters to position it. There are no refueling stations in space, so it is prudent to be smart about the weight of the design to ensure that the fuel does not run out. Size can be coupled with weight since the two are related. Just as with the weight, the larger a design is in physical size, the more expensive it is to launch. If it takes up a lot of space, there is less room for other cargo on the launch, thus making it more expensive. The size and weight of the design also impact its gravitational interaction with objects it travels in proximity to in space. This must also be considered for the designs thrusters needed to maintain proper trajectory.
As we have discussed here and in my last blog, the testing, screening, and qualification required for space products takes significant time. It is important to make sure that space grade components can endure the rigors of the harsh environment of space. I encourage you to look at the references below for more information on the various missions that I have included in the graph. It is amazing to see what man has been able to accomplish in space on these various missions. To get an idea of the types of components used in these kinds of applications, have a look at the space products on the Analog Devices web site. To see ADIís standard space products, please visit
Mars Exploration Rover
International Space Station
Mars Curiosity Rover
Parker Solar Probe
- Hubble Space Telescope
Analog ICs on Mars
EDN Exclusive: Meeting the Mars Rover 2020 Design Team at NASA JPL Caltech
Mission to Mars: NASA engineering and the Red Planet
NASA Cassini spacecraft crashes into Saturn: A failure or a calculated success?
NASA Juno electronics study Jupiter: Gravity Science Experiment
NASA Juno Spacecraft Radio
How Juno gathers solar power 588 million Km from the Sun
International Space Station (ISS) power system
NASA JPL spacecraft assembly building: Mars 2020 Rover
Mars Curiosity Rover: ChemCam laser-induced breakdown spectroscopy unveiled
Mars Rover ChemCam fires first laser on Mars
Curiosity Rover lands on Mars, August 6, 2012