Building rockets is no easy task. Different sections tend to refuse to fit together, wires are prone to somehow becoming both tangled and loose simultaneously, and even if everything else goes well – sometimes the parachutes just don’t deploy. Although failures can be demoralising, it is by failing that we learn quickest, and at GU Rocketry our past failures provide excellent lessons for our future projects. A key way to prevent failures is a robust design process; one where details reign supreme and the “worst case” scenarios have been predicted, simulated and mitigated. This is often referred to as mission design, which is “the definition of mission parameters and the refinement of requirements so as to meet the broad and often poorly defined objectives of a space mission in a timely manner at minimum cost and risk.” 2023 marks the start of our new streamlined design process, which combines the lessons learnt from Saltire-2 with the additional requirements placed upon us by the competitions we are attending this year. But what does this actually mean for us?
Broadly, the design process should encompass every stage of a rocket’s lifetime from the very first idea all the way to a successful recovery. The design process begins with the mission statement – a brief paragraph detailing the purpose of the rocket – which is expanded on in the mission goals. This is a short list of bullet points describing the rocket's aims that can be “ticked off”. Across the whole design process, it is very important that all goals and requirements are easily verifiable – let’s look at an example from NASA’s Space Shuttle Program:
“Space Shuttle Mission Statement – The NASA Space Shuttle shall operate as a Crewed Reusable Launch Vehicle (CRLV) with a fifteen-foot by sixty-foot payload bay to establish US assets in Low-Earth Orbit. It shall have a total of 65,000 pounds of easterly LEO payload lift capacity (40,000 pounds of polar lift capacity) and a cross range of 1,100 nautical miles to accommodate a wide range of payloads and mission profiles.”
The mission goals are essentially the mission statement codified into a list, with each goal unique, distinct, and easy to validate. What is especially important at this stage is to not let a final design (that you may already have in your head!) drive how you write your mission overview. The design process should never exclude any valid solutions in favour of what you might think is the best idea. It is also worth bearing in mind that mission goals do not have to be complicated! Here’s my favourite, and the only, mission goal from Apollo 11:
“NASA Office of Manned Space Flight Primary Mission Objectives for Apollo 11: Perform a manned lunar landing and return.”
The next stage is to identify any constraints that may affect your design – be this financial, practical, or sensible, it is important to create these hard barriers that can limit your design. Examples may include your choice of motor size based on availability or legality or the length of the rocket based on the launch rail you are using. The constraints then form the first of your requirements.
Requirements are sort of like an exam paper. They ask the questions that your design is supposed to provide the answers to – although very rarely do students write, answer, and then mark their own exam papers! Requirements are the backbone of any design and turn broad objectives into precise numerical statements that can be measured and aimed towards. Requirements should use specific terms, and be easy to understand and verify, and be objective rather than operational. This means you must state what is needed, not how it is achieved. The requirements, including ones imposed by any competition rules, are compiled in a long spreadsheet we refer to as the Specification (or the SPEC to its friends). As part of our new design process, the writing and verification of requirements fall under the remit of our Assembly, Integration, and Test (AIT) Engineer – lucky them!
The next hurdle for any budding launch vehicle is the Preliminary Design Review (PDR) – where we present our requirements and the initial design to alumni, academics, and members of industry to get their thoughts. Have we correctly identified the problem? Does our design meet the requirements? Have we missed anything? Invariably we have missed something, and I would like to quickly thank our review panel for their tireless help in making sure our rockets fly year after year – we couldn’t do it without you! Once these issues, known as Review Item Discrepancies (RIDs) are resolved, we move on to the Critical Design Review (CDR) phase. This is where the Saltire-3 and Mach-23 Competition Teams are at the time of writing.
CDR brings a host of new challenges – we know our rough design works, but how will it fit together? Can you tell me the weight of every single nut, bolt, washer, and wire we’re going to use? What about if one of them is loose? CDR requires a lot of work from our teams but ensures that our designs are safe, practical, and effective. We’ll be meeting with our review panel again in a few months for the CDR, before heading to part procurement, manufacture, and assembly. We’ll be sharing lots of updates during this phase, so stay tuned to hear all about the practical side of our work!
The Flight Readiness Review (FRR) comes a few days before the rocket launches and is a final check – subassemblies are assembled, batteries installed and charged, and the vehicle is raised on the rail. Once we’re confident in the full vehicle, it comes time to install the motor and parachutes, retreat to a safe distance, and press the big red button! We’ll be launching plenty in 2023, with teams at Mach-23, the European Rocketry Challenge, as well as launching here in Glasgow at the Fairlie Moor site. We hope to see as many of you as possible on the road, and I’ll sign off with a quote from John Glenn, the first American in space, who despite his reservations was kept safe by a robust design process:
“I felt exactly how you would feel if you were getting ready to launch and knew you were sitting on top of 2 million parts – all built by the lowest bidder on a government contract.”
For any further reading, these two books are the backbone of modern space design:
Larson, W.J, Wertz, J.R., et al., Space Mission Analysis and Design, Vol. 3, Springer 1992
Kapurch, S.J., NASA systems engineering handbook, Diane Publishing, 2010