ON HER second morning in space, was filled with excitement. She slipped out of her sleeping bag and somersaulted effortlessly through the Soyuz spacecraft. Then it all went horribly wrong.
Her head and back throbbed with pain owing to the effects of weightlessness. Even the slightest movement made her feel sick. The joy of watching Earth spin was replaced with a much stronger emotion. The telecoms entrepreneur, who had paid $20 million to become one of the first space tourists, couldn’t wait to get off.
Leaving wasn’t an option, of course. Ansari had to tough out the rest of the 50-hour journey rolled up in a sleeping bag with her head pushed against cargo destined for the International Space Station (ISS).
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That was back in 2006 when a trip to the ISS took two days and involved 34 laps around Earth. Earlier this year, though, a pioneering crew made the same trip in just under 6 hours. And in May, a second crewed mission shaved a further 7 minutes off the journey time, setting a new ISS-rendezvous record.
Faster hook-ups have an obvious benefit. The crew spends less time in the cramped confines of the vehicle, which has been compared to flying inside a high-tech phone booth. “If you’re having trouble acclimatising to space, it’s nice to have some extra time to get used to it, and that’s easier on the station than in a cramped spacecraft,” says five-time US space shuttle astronaut Jeffrey Hoffman.
Shorter flights could make crews more alert, and less time in transit means that astronauts can get down to their busy ISS schedules more quickly. Meanwhile, back on Earth, mission planners are learning valuable lessons that will further our ambitions to explore the wider solar system.
So how did mission controllers manage to slash 44 hours off the journey? And why? The motivation came not from space professionals, but tourists like Ansari. “For them, getting to the ISS as quickly as possible was very important,” says of Rocket and Space Corporation Energia in Korolev, Russia, and one of the architects of the .
The concept is nearly as old as the space age. In the 1960s and 70s, the US and Soviet space programmes vied to dock with orbiting vehicles in the fastest possible time (see “The other space race“). These “quick profile” schemes were also used to reach the Skylab and Salyut orbital laboratories. But with the arrival in orbit of the Russian , space travellers were shunted into the slow lane.
Any spacecraft that aims to dock with an orbiting craft is playing a game of catch-up. The early autonomous vehicles that NASA and the Soviets used to practise their docking manoeuvres were launched just ahead of their chasing spacecraft, making it easier for ground control to plot an intercept trajectory.
Mir, which became operational in 1986, was much larger and harder to manoeuvre; its orbital position had to be precisely tracked, and the station raised or lowered to meet incoming spacecraft. Allowing two days for mission controllers to complete these manoeuvres offered far more time to compensate for any errors.
Space fling
What Mir started, the ISS continued when it hosted its first crew in 2000. But with interest in space tourism hotting up, plans to revisit the quick profile scheme began three or four years ago, says Murtazin.
Even so, it took a while to convince US and Russian mission planners to give them a go, not least because the sequence of propellant “burns” needed to properly position the ISS for quick rendezvous had to be initiated six months in advance of the Soyuz launches. And had there been any system malfunction or last-minute orbital debris in the picture for either the ISS or Soyuz, the quick profile sequence would have been scrapped for the longer ride.
When it comes to connecting two vehicles in orbit, mission planners must consider the interrelated effects of atmospheric drag, gravity and thrust. Speed is also an issue: any vehicle launched from Earth has to catch-up with the ISS travelling at 28,000 kilometres per hour. If a chasing vehicle flies too high, too fast, it risks overshooting the station, which is why spacecraft typically use multiple orbits to loop their way up to the station and gradually match its speed.
Mission controllers decided to test the quick approach in 2012 with the automated Russian spacecraft, which takes supplies, not people, to the ISS and helps to maintain its orbit. The tests took just four orbits and were so successful that mission control gave the green light for doing the same thing with the Russian Soyuz craft that carry crew.
Murtazin points out that the quick profile Soyuz flights saved an estimated 20 kilograms of propellant per mission. That might not sound like much, yet it amounts to 8 per cent of the vehicle’s total fuel supply – a number that has caught the eye of mission planners everywhere. For them, conserving propellant potentially means reducing launch mass and that has beneficial knock-on effects – reducing mission costs and improving efficiency.
Nowhere does this matter more than for deep space missions, which are focused on both cost savings and more on-board space for scientific instruments.
As with orbital launches, planning the trajectory of deep space missions is getting more complicated. A case in point is the European Space Agency’s , which is scheduled for launch in January 2017.
Solar Orbiter will conduct a close study of the solar wind and the sun’s magnetic field, particularly around its little-understood polar regions. To do this, it will need to get closer to the sun than any previous spacecraft, approaching to within 42 million kilometres – not even sun-baked Mercury gets so near.
Planning Solar Orbiter’s trajectory began nearly a decade ago, says ESA mission analyst José Manuel Sánchez Pérez. “We need to get close to the sun, very close.”
Manoeuvres in the dark
The route that Sánchez Pérez and his colleagues have calculated affects everything from the choice of power systems and heat shielding to which instruments, and how many of them, Solar Orbiter can carry.
Getting it right is crucial. If there is a malfunction on the spacecraft or it is launched into the wrong initial orbit, Solar Orbiter’s relatively puny ion propulsion system might not pack enough punch to get it back on course. The result could be an expensive spacecraft drifting uselessly through the solar system – or ending up too close to the sun itself, resulting in a long plunge to a fiery death.
Above all, the route has an impact on Solar Orbiter’s cost. In theory, you can build a spacecraft with enough on-board oomph to reach the sun and orbit at such a close distance. The trouble is you need so much energy that the launcher would be huge and so would its cost. “This isn’t a feasible option for us,” says Sánchez Pérez.
What is feasible is using what the solar system already provides: free energy courtesy of the planets’ gravitational pull, and using a process known as a .
A spacecraft directed close to a planet or a moon can use that body’s gravity to redirect and boost its flight. NASA’s Voyager 1 and 2 spacecraft are famously nearing the edge of the solar system thanks to several gravity assists from Jupiter and Saturn, which are enormous sources of gravitational energy.
The plan for Solar Orbiter involves two fly-by boosts from Earth and up to six from Venus, depending on when the spacecraft launches. “Every time we perform one of these gravity passes we get closer to the sun, which is our goal,” said Sánchez Pérez.
Missions designed around gravitational boosts do have drawbacks compared with the more expensive options, such as carrying a lot of propellant or launching on a heavy booster rocket. The mission design is more complex and operations are less flexible. “In flight, we wouldn’t want to change anything unless absolutely required,” Sánchez Pérez says.
The biggest drawback to gravity-assist missions is that they generally take longer. Unlike the Soyuz quick profile flights, Solar Orbiter depends almost entirely on taking longer to get from here to there. One look at the meandering, sling-shotting voyage designed for Solar Orbiter shows it is akin to the interstellar version of a ballroom dance diagram (see diagram).
Because of this, Solar Orbiter won’t reach its operational orbit until about three years after launch. Once that orbit is established, the spacecraft is designed to function for another three to four years.
Clever trajectory design will also play a crucial role in any human mission beyond Earth orbit. Earlier this year, space tourist and entrepreneur Dennis Tito announced plans to send a two-person mission to Mars through the newly formed , which he is largely bankrolling. Tito is emphatically targeting a launch date of 2018 when the relative positions of Earth and Mars make for an unusually short journey.
The proposed trajectory for the Inspiration Mars mission – a fly-by that will give humans a close look at the Red Planet, but not a landing – is a “free return”.
The spacecraft would first use solar gravity to fling it towards Mars, where it would come within 160 kilometres of the planet’s surface. That fly-by doubles as a Martian gravity assist manoeuvre that will help propel the spacecraft back towards Earth.
Tito himself will undoubtedly have something to say about the spacecraft’s trajectory design: before making billions in the financial sector, he worked at the in Pasadena, California, where he helped to plot the trajectories of the Mariner spacecraft that explored Venus and, yes, Mars.
Tito is adamant that the Inspiration Mars mission will not only have a US crew but will also use the country’s rockets, whether tried-and-true workhorses like the Atlas or Delta, or the Falcon Heavy launch system being developed by SpaceX of Hawthorne, California. But Tito’s mission might just benefit from the Russian know-how behind the recent Soyuz quick profile flights.
One launch scenario for the Inspiration Mars mission would first launch a propellant tank into orbit, to dock with the crew vehicle to transfer fuel. The faster and more efficiently that docking happens, the sooner humans are on their way to Mars.
In the meantime, future orbital travellers – whether tourist or professional – can look forward to quicker trips, perhaps sparing their ground controllers that eternal refrain: are we nearly there yet?
The other space race
Rivalry during the 1960s between the US and Soviets also extended to docking in space
The US set the crewed record in 1966 when Pete Conrad connected the Gemini 11 he was travelling in with Richard Gordon to an uncrewed Agena target vehicle a mere 94 minutesafter launch.
The Soviets set the absolute record in 1968 when the Kosmos 212 and 213 vehicles docked just
47 minutes after launch. Both Kosmos spacecraft were uncrewed.
This article appeared in print under the headline “You take the high road”
