Koki Ho, assistant professor of aerospace engineering at the University of Illinois. Source: University of Illinois Department of Aeropspace Engineering

Elon Musk says that he wants to develop regular space travel for humans within his lifetime. This may seem like a daydream, but researchers are actually closer than ever to making regular space travel a reality. But space travel and efficiency don’t exactly go hand in hand. Koki Ho, University of Illinois assistant professor in the Department of Aerospace Engineering, and his team of graduate students are starting to tackle this problem. They researched ways to integrate logistics of space travel by focusing on lunar mission campaigns, spacecraft design and ways to optimize fuel and other space travel-related resources.

Ho believes that means finding a balance between time and the amount of fuel required. If people want to get to space faster it requires more fuel, but if time isn’t an issue, then slow and efficient low-thrust propulsion has proven to be a better option. Ho says that there are plenty of opportunities that are not being taken advantage of to minimize launch mass and cost of space exploration.

"Our goal is to make space travel efficient," Ho said. "One way to do that is to consider campaign designs, that is, multiple missions together--not just launching everything from the ground for every mission like Apollo did. In a multi-mission campaign, previous missions are leveraged for subsequent missions. So if a previous mission deployed some infrastructure, such as a propellant depot, or if work had begun to mine oxygen from soil on the moon, those are used in the design of the next mission."

Data from past missions that were successful or at least planned were used to create the simulated models of a combined campaign. The model can be customized for various possibilities including heavier or lighter spacecraft, a specific set of destinations, number of people on board and more.

"There are issues with the vehicle sizing," Ho said. "In our previous studies, in order to make the problem efficiently solvable, we had to use a simplified model for the vehicle and infrastructure sizing. So creating the model was fast, but the validity of the model wasn't as good as we desired."

In one of their studies, Ho and his team focused on a fidelity issue that popped up in the past simplified models. They created a new method to simulate a more realistic mission and vehicle design models with a computational load that has a reasonable level.

"In this research, we are designing the vehicles from scratch so that the vehicle design can become part of the campaign design," Ho said. "For example, if we know we want to send a human [to] Mars by the 2030s, we can design the vehicle and plan the multi-mission campaign to achieve the maximum efficiency and the minimum launch cost over the given time horizon."

The study uses the concept of propellant depots in space, which has been considered by scientists for a few years.

"There are questions about how efficient the depots actually are," Ho said. "For example, if it takes the same or more amount of propellant just to deliver the depot then what's the point of sending it ahead?"

This research proves that a combination of high-thrust and low-thrust propulsion systems are the key to finding a solution to this question.

"A preparatory mission might be conducted beforehand to deliver into orbit mini-space stations that store fuel, cargo or other supplies," Ho said. "These crafts can be pre-deployed so they are orbiting and available to a manned spacecraft that is deployed later. The cargo/fuel spacecraft can make use of low-thrust technologies because the time it takes to get to its destination isn't critical. Then for the manned spacecraft, we'd use high-thrust rockets because time is of the essence when putting humans in space. This also means that because the fuel is already at these space stations, the actual manned ship doesn't have to carry as much fuel."

The paper on this space exploration research was published in the Journal of Spacecraft and Rockets.