Andreas Hein describes how an i4is technical team responded to the detection of the interstellar asteroid ’Oumuamua. Their paper, Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid received wide attention and sparked interest in interception of interstellar objects.
In 2017, a yet unseen, mysterious visitor from our galaxy has entered our solar system. On October 19th 2017, the University of Hawaii’s Pan-STARRS 1 telescope on Haleakala discovered a fast-moving object near the Earth, initially named A/2017 U1, but now designated as ’Oumuamua . The object’s trajectory is hyperbolic, which means that it is not bound to the solar system. It flew into the solar system from interstellar space and after having been pulled close to the Sun by its gravity, it is now on its way of leaving it again. At its closest approach to the Sun, it had a velocity of over 80 km/s, faster than any object that has been observed in our solar system to date. At this speed, you would get from the Earth to the Moon in 1.3 hours. Its speed will gradually decrease while leaving the solar system and finally reach about 26 km/s in interstellar space, when it has left the Sun’s gravitational pull.
But this is not the only novelty. It gets far more mysterious. The luminosity change pattern of ’Oumuamua over time indicates that it has a remarkable shape, never observed before in a small body: It looks like a cigar and has roughly the length and width of the Empire State Building.
Another mystery: We still do not know what ’Oumuauma actually is. Is it a comet or an asteroid? First observations indicated that it didn’t develop a cometary tail when it approached the Sun, which means that it is an asteroid. But later publications hypothesized that if ’Oumumamua has travelled through interstellar space for millions of years, it might have developed a “crust” around a potentially icy core, which might explain why no tail was observed. The crust prevented a tail to form.
From the beginning, discussions about a non-natural origin of ’Oumuamua abound. Due to its odd shape and trajectory, there was a very low probability that this object is actually of artificial origin. A low probability by very high impact event merits further investigation and therefore Breakthrough Listen attempted to capture signals that might be emitted by ’Oumuamua, to no avail.
At this point, it should be clear that ’Oumuamua is probably one of the most exciting objects that were discovered in 2017 and since its discovery, one question has been repeatedly asked: Can we get there? And can we get there with current or near-future technologies? These are exactly the questions the team from i4is asked itself. We immediately formed a team of volunteers (Kelvin Long, Nikolaos Perakis, Robert Kennedy, Richard Osborne, Andreas Hein) on the 31st of October, 12 days after ’Oumuamua’s discovery and baptized the project “Lyra”; the star constellation in the direction from which ’Oumuamua came from. Intense design activities started during which further external people joined our efforts such as eminent astronomer Marshall Eubanks and former Ariane 4 guidance engineer Adam Hibberd. What we wanted to know is if we can get to ’Oumuamua within a reasonable timeframe of a few decades with a launch in the next 5-10 years. That much time is realistically the minimum duration for developing an interplanetary spacecraft.
Regarding the first question we wanted to answer, the simplest way of approaching this problem is to assume that ’Oumaumua travels at 26 km/s and now you need to chase it. The later you start the chase, the faster you need to be, as ’Oumuamua will fly farther and farther away from us. The farther ’Oumaumua is away when a spacecraft reaches it, the more difficult will it be to observe it. ’Oumuamua is a very faint object and the farther it gets from the Sun, the more and more difficult will it be to collect light that is reflected from it, which means you need a larger telescope that can collect more light with a larger lens diameter. Another disadvantage is that the longer you have to wait for the scientific data to return, the less interesting it gets for scientists to promote a mission. Developing an interplanetary spacecraft already takes about a decade. If it takes further 30 years to get the data, a young scientist is essentially close to retirement when the data arrives.
We can easily visualize this problem. With a time-distance graph, as shown in Figure 1, you can easily see that there are infinite possible trajectories that will reach ’Oumuamua sooner or later. What we do as engineers is to select realistic constraints in order to select the more realistic options. You can easily cut the graph on the x-axis (time) and define the latest and earliest date you want to launch the probe (between 2013 and 2028). When you do this, you can immediately see when you will reach ’Oumuamua (one to a few decades) and at which distance (100s of astronomical units). The slope of the curve is the required velocity (40, 50, 60 km/s) for reaching ’Oumuamua at a specific time and distance.
Now, the obvious challenge is to reach the required velocities of several dozens of km/s. You need a lot of energy for that. The fastest human-made object is Voyager 1 with a current velocity of about 16.6 km/s at a distance of 122 AU. We need to be several times faster than that. Although challenging, there are ways of reaching such high velocities using existing and near-future technologies. In the following, I present three possibilities that we have considered in the paper.
For the first option, we use a mission concept that has been previously proposed by a Keck Institute for Space Studies report for exploring the interstellar medium. It is essentially a rollercoaster ride The spacecraft is first sent on a trajectory out of the Earth’s gravitational field using a large rocket, for example the Falcon Heavy, Space Launch System, or the Big Falcon Rocket. The spacecraft is accelerated to such high velocities that it is not only thrown out of the Earth’s gravity field but has enough energy to fly out to Jupiter. At Jupiter, the planet’s gravity decelerates the spacecraft with respect to the Sun. This maneuver is called “sling shot”. The advantage is that it can be used for accelerating and braking spacecraft by using the planet’s gravity. Hence, you get this acceleration and deceleration “for free” without using propellant. The acceleration and deceleration is achieved by a tiny reduction or increase in the orbital energy of the planet. As the mass of the planet is vastly higher than the mass of the spacecraft, it is essentially negligible. To continue, our spacecraft has been decelerated so much by exploiting Jupiter’s gravity field that it is now on a trajectory that it is falling towards the Sun in an almost straight line, an extreme roller coaster ride, although it takes over a year to fall. Of course the spacecraft will not fall into the Sun but would move away from the Sun once it has passed its closest point to the Sun. The spacecraft gets very close to the Sun, about 3 solar radii or about 1.5 million km. At such a distance, the solar radiation is about 20,000 times higher than what you receive during a sunny day. Converted to Watts per square meters, the power per area is about 15 MW / m². This is higher than the power per area inside a fusion reactor. To avoid that the spacecraft melts away, a heat shield is used which is similar to the heat shield of the NASA Solar Orbiter mission, which fill fly close to similar distances to the Sun and is currently undergoing testing. Now, at the closest point to the Sun, the spacecraft ignites a solid propellant engine it has been carrying all its way. In orbital mechanics, you get the biggest “bang for the buck” for a rocket engine, if you ignite it at the closest point to the central body. Hence, the whole idea of falling so closely to the Sun is to ignite the engine at the closest point of approach and then to be propelled away from the Sun with the maximum “bang”. The spacecraft flies away from the Sun at the incredible speed of about 370 km/s. At this speed you would get from London to New York in 15 seconds. Note that this is the speed you would need for a mission duration to ‘Oumaumua in 8 years and a launch in 2021. The spacecraft will have a velocity at infinity of 55 km/s and is therefore much faster than ‘Oumuamua with 26 km/s. The spacecraft would fly pass ‘Oumuamua in 2029, taking images using a telescope at a distance from the Sun of 69 Astronomical Units (Earth-Sun distances). At this point ‘Oumaumua will be a black object in front of the blackness of space. Where the human eye would fail, a telescope and other instruments will suck in the electromagnetic waves that are nevertheless emitted by ‘Oumuamua. The data will then be sent back to Earth with an antenna powered by nuclear radioisotopic generators, a chunk of Plutonium whose heat is transformed into electricity. Finally, the data is transformed into images. What will we see?
It is important to note that all technologies that are used for this mission concept already exist today. The Falcon Heavy is scheduled for a launch in 2018, the heat shield will soon be launched into space with the Solar Orbiter probe, solid rocket engines are routinely used in space, and the spacecraft itself could be based on the heritage of the New Horizons probe that has flown past Pluto.
An alternative to this “conventional” mission is to use more advanced technologies. “Advanced” means here that these technologies have not yet been flown in space but laboratory experiments have shown that they work in principle. One possibility is to use laser sail-propelled spacecraft. Laser sail-propelled spacecraft use a laser sail, which is essentially a thin, reflective surface that reflects the photons of the laser beam. The photons exchange momentum with the sail and the spacecraft is accelerated. Think about a sail ship and replace the wind by photons and the sail by a reflective surface. In 2016 Breakthrough Starshot has announced the development of a laser-sail propelled interstellar mission, based on a terrestrial laser infrastructure with a beam power of several dozens of GW and gram-sized spacecraft that are accelerated to 20% of the speed of light. Now, could we downscale this infrastructure to launch a spacecraft to ‘Oumuamua? The spacecraft would be launched into space, maneuvered into the line of sight of the laser infrastructure based on Earth and are then “shot” away by the laser. We did calculations on such a modified infrastructure. It turns out that a 2 to 4 MW-class laser infrastructure would be sufficient to accelerate a one gram spacecraft to the same velocity at infinity as the sling shot mission. However, one gram is obviously not much. If we would like to launch a CubeSat-class (1kg, 10cm cube) spacecraft, we would need about 2 to 4 GW of laser power. But what’s the advantage of building a large laser beaming infrastructure to send a chip-sized or a 10cm cube to ‘Oumuamua? First, this could be an opportunity for a mission that can be done with a smaller version of the Starshot beaming infrastructure, providing a justification for these intermediate infrastructures before the full-scale interstellar-capable infrastructure is operational. Second, the real advantage is the flexibility of such an infrastructure of launching spacecraft to promising targets without much advanced warning. Imagine a “mothership” with 3-4 CubeSats in space. Once the next interstellar asteroid is detected, the mothership releases the CubeSats which are then launched towards its target within days, thereby minimizing the time between discovery and data return. Compare that with the mission based on conventional technologies before. It takes years to perform the manoeuvres to get the spacecraft up to speed.
Let us summarize. As you have seen, there are ways of flying to ‘Oumuamua. We could either use existing technologies or technologies that are currently under development. Who will be first to unravel the secrets of ‘Oumaumua? Or will we be too late? In that case, let us prepare for the next interstellar object!
The Lyra paper is Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid, Andreas M Hein, Nikolaos Perakis, Kelvin F Long, Adam Crowl, Marshall Eubanks, Robert G Kennedy III, Richard Osborne arxiv.org/abs/1711.03155
Read more on our Project Lyra page.
About Andreas Hein and the team
Dr Andreas Hein is Executive Director of the Initiative for Interstellar Studies (i4is) and chairs its technical committee. His PhD is from the Technical University of Munich (TUM). He is a Researcher / System Architect - Autonomous Driving System of Systems at CentraleSupelec, Paris.
Kelvin F Long is President of i4is and founded the organisation with Rob Swinney in 2012. He is the author of Deep Space Propulsion: A Roadmap to Interstellar Flight (Springer, 2012) and is a member of the Advisory Committee of Breakthrough Starshot.
Robert Kennedy is President of i4is-USA. He is Senior Systems Engineer at Tetra Tech and co-founded the Tennessee Valley Interstellar Workshops (TVIW).
Marshall Eubanks is CEO at Asteroid Initiatives LLC, the Asteroid Prospecting Company, and has held senior positions at JPL and the Internet Engineering Task Force (IETF).
Nikolaos Perakis is a postgraduate at TUM working on a PhD in combustion modelling and simulation of rocket engines.
Richard Osborne is a Systems Consultant and rocket scientist. He has worked for many companies in space technology including Reaction Engines and Commercial Space Technologies. He is a Council Member of the British Interplanetary Society.
Adam Crowl is Project Officer at Queensland Health, Australia. He is the author of numerous papers on interstellar flight and was a member of the original Project Icarus study group.
Adam Hibberd is a freelance software engineer and musician/composer. He worked on software for Ariane 4 guidance and Airbus flight simulation at EASAMS and other aerospace companies.
Kieran Hayward is an Avionics Validation Engineer at Thales Alenia Space UK. He has an MSc in aerospace engineering from Cranfield University.