Week 4: Spacecraft Propulsion & Design Inspiration
Kira A -
Long time no see (or blog) everyone đ . I hope you are all prepared to launch right into the updates for this week! While I would love to say that I have been hard at work these past five days beginning to write the code for the orbit-raising maneuver as I had planned, due to my travel and unexpected sick days, I was not as efficient as I had hoped I wouldâve been. I recognize that this project will not always go according to plan. Still, I am grateful for the opportunity to experience both its positives and negatives as it is a learning experience that will prepare me for challenges I have yet to face in the future. I intend to use my recent experience as fuel to propel me to achieve more in the coming weeks. Now, if you havenât caught on to the hints, this blog is all about the spacecraft I will be using to model my mission and its propulsion system!
The Moon Bound mission focuses on the orbital mechanics and the maneuvers, specifically orbit-raising, needed to get to the Moon in the most efficient way possible; however, it is vital to discuss the spacecraft that I plan to use for the mission as it will be one of the many inputs for my system when I am finally able to model the maneuvers. And, I mean, come on, itâs not like itâs rocket science! But first, I think we should cover some of the spacecraft that I will be taking inspiration from when determining the specifications of my spacecraft. For this task, as to not lecture you all on the complete history of space missions in and beyond the cislunar region, I have chosen three spacecraft to discuss: the Dragon 2 capsule from SpaceX, the Mangalyaan-1 from ISRO, and the 2001 Mars Odyssey from NASA/JPL.
I have chosen these three spacecraft, among a few others, to model my spacecraft after due to the similarities in mission objectives that they share with my mission as discussed in my week 3 blog. First, the Dragon 2 capsule, or Cargo Dragon, is probably the most well-known spacecraft as it is the most recently developed and used – last launched May 11th, 2024. This vessel is specifically designed for cargo loads, aligning closely to my mission objective to transport cargo to orbit around the Moon from Earthâs orbit. The Dragon 2 capsule in its cargo configuration has no life support systems, seating accommodations, pilot interface, or lavatory, as it is not designed to have a crew and uses autonomous docking at the ISS (International Space Station). As my mission will not require a crew, my spacecraft will also not feature any of these design elements. Additionally, the Dragon 2 can transport powered cargo using its solar panels, aiding in long term storage of perishable items throughout its missions. Lastly, the Dragon 2 bolsters the Draco thrusters which we will dive into more detail about later when we discuss the propulsion system of my spacecraft.Â
Next up is the Mangalyaan, or Moon Orbiting Mission (MOM) from ISRO. I took inspiration from this mission because it is the cheapest interplanetary mission to have ever been completed at a mere 73 million USD, which is a small sum in comparison to 297 million USD used for the 2001 Mars Odyssey that we will talk about next. As optimizing mission costs is a big objective of the Moon Bound mission, this mission is a big inspiration for much of the work in my project. I will further analyze the steps that ISRO took to reduce the overall cost of this mission, to hopefully implement them into mine.
Lastly, the 2001 Mars Odyssey: the longest continually orbiting spacecraft around a planet that is not Earth and the relay for communications between ground-based operations on Earth and Mars. The 2001 Mars Odysseyâs longevity and communication abilities stuck out to me as something to look into and replicate in my spacecraft. Furthermore, the mission entailed radiation analysis of the ânear-space radiation environmentâ around Mars for the risk it may post to explorers. This is something I would also like to implement into my mission as it will be the precursor to humans establishing a permanent presence on or around the lunar surface, and with that, it is necessary to ensure that we do not expose ourselves to excessive amounts of radiation in the process or long-term.
Finally, we have arrived at the hot topic of the blog: the propulsion system. Many factors determine how a rocket engine might be compatible with a certain spacecraft and its mission. Among these are its size, weight, fuel type, durability, and thrust. Size, weight, and durability are pretty self-explanatory, however, fuel type and thrust are more complicated. There are four main types of rocket engines most commonly used today for propulsion: liquid-fuel, solid-fuel, hybrid, and ion. The most commonly used rocket engine is by far the liquid-fuel engine, as it can be used in a wide variety of applications from launch vehicles to spacecraft attitude adjustments. Liquid-fuel engines use a liquid fuel and a liquid oxidizer that are both pumped into a combustion chamber and ignited, and from that ignition, the hot exhaust gas is expelled through a nozzle to direct the thrust. On the other hand, solid-fuel engines use a mixture of solid fuel and solid oxidizer that are burned to produce thrust. These are typically less expensive and more reliable than liquid-fuel engines but are not reusable. Now, as one can assume, a hybrid fuel engine is an engine that makes use of a combination of solid fuel and a liquid oxidizer. This makes them more efficient than solid-fuel rocket engines and more controllable and reliable (less components) than pure liquid-fuel rocket engines. Lastly, the ion engine is the least common out of these four engine types, but it is useful in specific applications. The ion engine uses electricity to accelerate ions, or charged particles, to high speeds and produce thrust. This thrust is very small but the engines themselves are very efficient, making them great for small spacecraft maneuvers or long duration impulses.Â
So, now that weâve discussed the four main different fuel types for rocket engines, what is all this talk about thrust? Thrust is dependent on many different factors, but at its core, thrust is the force that propels a rocket forward. By Newtonâs third law, every action has an equal and opposite reaction, so when the exhaust of an engine is pushed out from the spacecraft, the spacecraft is pushed forward by the exhaust. My spacecraft will not be doing any maneuvers that require absurd amounts of thrust, such as launches, as it will only be going between an orbit around the Earth and an orbit around the Moon. Beyond this, it will need to have reusable engines to make multiple trips and refuel, as well as the ability to store fuel for extended periods between maneuvers. For these reasons, I am considering implementing an engine similar the Draco thrusters from SpaceX for use on my spacecraft, as they are used in very similar applications. The Draco thrusters are hypergolic liquid rocket engines used on the Dragon 2 for orbital maneuvers and attitude adjustments. A hypergolic liquid engine, similar to a liquid engine, uses a liquid fuel and liquid oxidizer, however, the two spontaneously react when in contact with each other, eliminating the need for an external energy source to ignite them. Hypergolic fuels and oxidizers are easily stored as they do not need to be supercooled like other traditional liquid rocket fuels and therefore, do not need to have a separate cooling system on board that would increase the overall cost of the spacecraft. The monomethyl hydrazine fuel and nitrogen tetroxide oxidizer used in the Draco thrusters produces around 400N (90 pound-force) of thrust in a vacuum and has a specific impulse of 300s (specific impulse indicates the efficiency of the fuel per the amount of fuel being expended out of the rocket). These values, while having more official definitions and made relevant only in relation to other values for comparison, match well with what I am looking for from the engines on my spacecraft, which is why they are a candidate for the final engines I will end up using.Â
Unfortunately, as I will not be focusing on designing a novel propulsion system for my specific spacecraft and mission requirements, I will need to implement existing propulsion systems, which almost always have drawbacks in some aspect of the mission. One major con of the Draco thruster for implementation in the Moon Bound mission is that the hypergolic fuel it uses is highly toxic, requiring meticulous handling to ensure the safety of any personnel working with the fuel and crew on board the spacecraft. This training and extra time drives up the price of the mission significantly. However, because my spacecraft will not be manned, the toxicity once on board is not an issue to the crew but might still pose a threat to any biological matter being transported as cargo during spaceflight. The most significant problem arises with the cost of hypergolic fuels. Hypergolic fuels are among some of the most expensive rocket fuels and are therefore not compatible with my mission objective to reduce unnecessary expenses. So, this week I will dive deeper into more cost-effective alternatives for an engine such as the Draco 2 to implement into my rocket design.
Beyond investigating further options for my propulsion system, I plan to get back into MATLAB and work on the orbit-raising maneuver.Â
Thank you all for tuning in, and sorry for the lack of pictures this week đ Thank you to Dr. Goodwin, Mr. Joseph, and Dr. Farooq for your constant support and feedback. I look forward to managing my time better and making some more progress this week!Â
Ad Lunam!
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