Project Lyra was prompted by the question of the feasibility of a spacecraft mission to ‘Oumuamua, the first object to be discovered definitely originating from outside our solar system – the first of its party or interstellar scout as is implied by the Hawaiian translation of its name.
Many of you readers will have heard of ‘Oumuamua and know of its extraordinary, if not unique, properties as identified through observations as it passed through the inner solar system. It was only a pixel in telescope images taken both on Earth and in space, but much has been inferred from the data acquired.
The artist images which saturate the web are largely based on the supposition of a long cigar-shaped rocky kind of a body, despite excellent work having been conducted into analysis of its general shape from variation of reflected sunlight on its surface over time (its light curve), indicating it is more likely to have a flat pancake sort of a shape (Mashchenko 2019).
Just a close-up picture of ‘Oumuamua would suffice to answer a mountain of open questions as to the precise nature of this interstellar object which will never be resolved by any other means, ‘Oumuamua is way out of sight of any existing telescopes.
Before joining Project Lyra I had previously designed and developed some software – Optimum Interplanetary Trajectory Software (OITS) – which turned out to be ideal for investigation of missions to interstellar objects. ‘Oumuamua was discovered on October 19th 2017, by which time I had just about finished the development.
The precise trajectory needed to get to a celestial body depends intimately on the particular kind of propulsion deployed to get there. The propulsion assumed by OITS is any high thrust variety - this might be chemical rockets for instance. Thus OITS can be exploited to decide upon the feasibility of missions using current or soon-to-be-current propulsion technology (like the NASA Space Launch System) - chemical rockets are very much tried-and-tested technology.
The huge challenge of a direct mission to ‘Oumuamua using chemical was highlighted in the first Project Lyra paper (Hein et al. 2019) and this pretty well excluded a direct mission scenario as a viable option. Hence it turns out that to get there using rocket technology would need a couple of magic tricks which my software development, OITS, could demystify, so-to-speak.
The first is a technique which was discovered in the ‘60s by Michael Minovitch working at NASA Jet Propulsion Laboratory (JPL). It is known as the Gravitational Assist (GA) and has been demonstrated in many historical interplanetary missions (such as the Voyagers, Galileo, Cassini, New Horizons, etc) and no-doubt will be exploited in many future missions also. A GA is where the interplanetary spacecraft encounters a planet and is accelerated/decelerated to a higher/lower speed by ‘stealing’ some of the planet’s kinetic energy, without the spacecraft needing to expend any extremely precious on-board propellant.
The second trick was discovered by German scientist Hermann Oberth, and is therefore called the Oberth Effect. It is unlike the pure GA as it requires a burn of the chemical rockets. Oberth stipulated that to get maximum benefit from the propulsion system, this burn must be delivered at the spacecraft’s maximum speed. In a gravitational well (such as that generated by the sun or a planet for instance), this maximum occurs when the spacecraft is at the ‘periapsis’ point, the closest approach of the spacecraft to the gravitating body. My animation demonstrating a Solar Oberth can be found here.
So over the course of several articles on the subject of the feasibility of missions to ‘Oumuamua, lots of different permutations of
- pure GAs,
- Oberth Manoeuvres, and
- powered GAs (a combined GA and Oberth Manoeuvre),
were investigated.
Papers (Hein et al. 2019) (Hibberd, Hein & Eubanks 2020), concentrated on a particular sort of Oberth Manoeuvre - a solar Oberth (SOM) - which requires a close passage of the spacecraft by the sun and a correspondingly low perihelion (closest approach to the sun). Paper (Hibberd et al. 2022) was concerned with reaching ‘Oumuamua without the benefit of a SOM (so obviating the necessity for a massive and energy-expensive heat shield) but instead adopting a Jupiter Oberth (JOM). Thus this paper (Hibberd et al. 2022) largely exploits (3) above.
I now come to the crux of this article, as it is important to note that at this point in time and in general practice, interplanetary missions are restricted to unpowered flybys, i.e. option (1) above. This is because the two other options, i.e. some form of Oberth (2) or powered GA (3), can both be rather risky, requiring ongoing doppler measurements of the spacecraft received at Earth and a continuous communication link between ground stations and the spacecraft up to the point of delivery of the thrust in order to ensure the burns are delivered to exactly the right level of velocity increment, in the right direction and with the right timing. In turn this precision is needed due to the sensitivity of the subsequent trajectory to these factors. Therefore it so happens that this arrangement of timing and accuracy of the thrust vector is rather hard to achieve.
Does this make the research in the aforementioned papers irrelevant? The answer is no because these problems can be circumvented, by being more technologically ambitious and less safety-conscious, for instance by using autonomous GNC techniques which have yet to be generally established in interplanetary missions. However wouldn’t it be convenient if a mission to ‘Oumuamua could be discovered which did not require (2) and/or (3), but only utilised (1)?
In a previous blog, I have identified just such missions, using only (1) with a passive Jupiter encounter, but which have rather long drawn-out flight durations (40-90 years). So the natural question is whether there are any other options which would bring down this time, yet exploit only (1)?
To this end I conducted some investigations into missions which could possibly satisfy this requirement, and you know what? - I may have found an option which has hitherto remained in hiding. To be exact it does require a Jupiter Oberth Manoeuvre (JOM) but otherwise there are absolutely no burns required to get to Jupiter – all the encounters are (1) above.
I have written it all up in a paper which can be found as a preprint online - (Hibberd 2022). As of the time of writing of this blog the mission would launch in 4 years’ time, i.e. 2026.
To summarise it would utilise a V-E-DSM-E-M-J sequence, where those symbols are respectively Venus, Earth, a Deep Space Manoeuvre, Earth again, Mars, followed by Jupiter - subsequent arrival at ‘Oumuamua happening 30 or so years from now. All those initial 5 encounters from Venus to Mars inclusive require just about NO velocity increment from the rockets (ΔV) and so this amounts to a free taxi-fare to Jupiter. In fact to use this analogy precisely, there is an initial premium (the ΔV needed by the launch vehicle at Earth) followed by absolutely NO mileage rate, but an arrival charge at Jupiter whereupon fuel is required in the form of a JOM to accelerate the probe towards ‘Oumuamua. Refer to Figure 1 for the plan view of this trajectory solved by OITS.
The flight duration for this mission is rather protracted – 31 years – but actually would arrive only 5 years later than missions which utilise the SOM option and further it of course needs no heat shield. In contrast the non-SOM VEEGA scenario detailed in (Hibberd et al. 2022) has the drawback of needing a dedicated liquid propellant stage to deliver all the in-flight ΔVs – thus the aforementioned problematic (2) and (3) burns needed on the way. This also significantly complicates the spacecraft design.
Thus to conclude this V-E-DSM-E-M-J mission may come to the rescue of Project Lyra. For information on the sort of spacecraft masses which could be achieved via this V-E-DSM-E-M-J go to the preprint here and decide for yourself whether it would be worth-the-while.
You may be interested in an my animation of the trajectory:
Adam Hibberd
July 2022/Updated April 2024
Bibliography
Hein, AM, Perakis, N, Eubanks, TM, Hibberd, A, Crowl, A, Hayward, K, Kennedy III, RG & Osborne, R 2019, 'Project Lyra: Sending a spacecraft to 1I/'Oumuamua (former A/2017 U1), the interstellar asteroid', Acta Astronautica.
Hibberd, A 2022, 'Project Lyra: Another Possible Trajectory to 1I/'Oumuamua', arXiv.
Hibberd, A, Hein, AM & Eubanks, TM 2020, 'Project Lyra: Catching 1I/‘Oumuamua – Mission opportunities after 2024', Acta Astronautica, pp. 136-144.
Hibberd, A, Hein, AM, Eubanks, TM & Kennedy III, RG 2022, 'Project Lyra: Mission to 1I/'Oumuamua without Solar Oberth Manoeuvre', arXiv.
Mashchenko, 2019, 'Modelling the light curve of `Oumuamua: evidence for torque and disc-like shape', Monthly Notices of the Royal Astronomical Society, vol 489, no. 3, pp. 3003-3021.