Space Sunday: orbits, landings, launches and a portrait

As I noted in my previous Space Sunday update, Mars is having one of its busiest period in the 50 years we have been sending probes to either orbit or land on that world, with no fewer than three new robotic missions either now in orbit or about to arrive.

The reason for this rapid-fire arrival is simple: Mars and Earth both orbit the Sun, but Earth, as the nearer of the two, completes a single orbit once every 365.25 days whilst Mars does the same once every 687 days. This means that Every so often, Earth “overtakes” Mars as they circle the Sun.

These periods of “overtaking” occur once every 26 terrestrial months,  and are – slightly confusingly – called periods of “opposition”,  so-called because Mars and the Sun appear to be on “opposite” sides of the Earth relative to one another in their orbits. However, where space missions are concerned, it’s not the point at which Earth “overtakes” Mars that is important, but the period of a couple of weeks beforehand, when Earth is in the final stages of “catching up”.

It is at this point that a mission to Mars can be most effectively launched. This is for a number of reasons: firstly, it marks the time when Earth and Mars are relatively close to one another in their respective orbits – perhaps as close as 50-60 million km when measured in a straight line. While spacecraft do not travel in a straight line between planets, it does mean the distance they do have to traverse is reduced to a few hundred million kilometres. Secondly, launching while Earth is still “catching up” with Mars means a spacecraft receives an added “boost”. Thirdly, it ensures the vehicle can enter a Hohmann Transfer orbit between the two planets.

Named for German engineer Walter Hohmann, who first calculated it in 1925, the Hohmann Transfer Orbit is the most fuel-efficient means for a spacecraft to move between the orbits of two different planets, further reducing the complexity of the journey by reducing the number of mid-course corrections that might otherwise be required. When taken as a whole, these three points mean that a mission to Mars can be launched with the minimum amount of time it needs to reach its destination and in a manner that maximises fuel efficiency.

Because the orbit of Mars is more elliptical than Earth’s, the actual time it takes to travel between the two during these periods can vary between six and seven months., with the distance this time meaning that the three missions launched in July 2020 have taken almost seven moths to reach Mars. They form an international flotilla, as I noted in my previous Space Sunday update, being from the United Arab Emirates by way of Japan, China and the United States.

All three are highly ambitious in nature, again as I noted last time around. The UAE’s Hope mission, the first to arrive, marks both the country’s first attempt to reach Mars and its very first interplanetary mission as a whole – no mean achievement for a country that has only recently committed itself to the goal of long-term space exploration and science.

The mission itself has been put together and is being run by a team of around 150 and at a cost of just US $200 million – which, as the saying goes, is just peanuts for space [missions]. It utilised a Japanese H-IIA launch vehicle to reach Mars, and in the face of understandable nervousness within the Hope mission team, the roughly cubic vehicle with a mass of around 1.4 tonnes, lipped into its initially orbit around Mars on Tuesday, February 9th following a 27-minute continuous burn of the vehicles main thrusters, a manoeuvre that used around half the craft’s available fuel load.

As it did so, the UAE staged a national celebration, with images of the Martian moons of Phobos and Deimos being projected into the night sky over the desert, while the skyline of Dubai saw buildings lit up with the mission name and images of the planet.

The aim of the mission is to further understand the Martian weather, atmosphere and climate, and to specifically close existing gaps in our knowledge of all three. It occupies what is called a high supersynchronous orbit, circling the planet once every 55 hours at a distance of between 20,000 km (periapse) and an apopapse of 43,000 km, altitudes that allow it to observe daily cycles across the entire visible hemisphere of the planet and witness season changes as they affect both the northern and southern hemispheres.

The following day, China announced the successful orbital insertion of its first mission to Mars, the highly ambitious Tianwen-1 multi-mission. Comprising an orbiter vehicle, a lander and a rover, the mission marks China’s first attempt to reach Mars, although it will be another few months before the lander and rover descend to the surface. This is to allow a full survey of the proposed landing zone on Utopia Planitia to be completed using the orbiter’s high-resolution camera systems. In addition, the orbiter will be carrying out its own science surveys of the planet.

During Tianwen-1’s approach to Mars – which it orbits far closer than the Hope mission – the mission team activated the orbiter’s low-resolution engineering cameras. Designed to allow the mission team to examine various element of the vehicle – its propulsion module, the solar panels, etc., the camera were allowed to run for 30 minutes during the orbital insertion, taking images every three seconds. These images were then edited together to produce a short film of the mission’s arrival at Mars.

However, media interest is most focused on the forthcoming arrival of NASA’s Mars 2020 mission, which is due to take place on Thursday, February 18th and by its very nature, is bound to be the most exciting. Comprising the rover Perseverance and mini-drone Ingenuity, there will – again as I noted last time around – be no gentle easing into an orbit around Mars.

Instead, and protected by an aeroshell and heat shield, the craft will slam into the Martian atmosphere, using the friction of its massage to initially decelerate before turning to parachutes to ease down through the atmosphere to a point where a rocket-propelled “skycrane” will take up a hover and lower the rover and the drone attached to it to the ground before flying off to its own destruction.

It’s a similar method to that used in 2012 to deliver the Mars Science Laboratory rover Curiosity to Mars – but there are some differences. Firstly, as well as taking images of its descent to landing, Mars 2020 will also record the sounds of its descent, with engineers hoping to hear the movement of air over the vehicle while it is on the way down, and even the sound of the rockets firing and the noise created as their blasts strike the ground.

More particularly, Mars 2020 will have a measure of being able to steer itself to a safe landing using a technique called Terrain Relative Navigation (TRN). originally developed for use with cruise missiles, it essentially uses a map of the proposed landing site with the known elevations of obstacles along the decent and landing path, which is directly compared with footage captured by the descent system cameras.

Due to the time delay in two-way Mars/Earth/Mars communications (some 14 minutes), this navigation will be carried entirely autonomously by the vehicle’s own computer systems. If the camera detect surface obstacles  that are not in keeping with the map, or which pose a threat due to their elevations exceeding those recorded on it, the computer will direct the landing systems to use their rockets to ease the vehicle away from the hazard. It’s also hoped that this system will allow Mars 2020 to achieve its landing point with a high degree of accuracy – again allowing for any last minute  unexpected hazards the system may pick up that require it to divert by a few metres.

If all goes as planned, the rover and drone should reach the surface of Mars at around 20:55 UTC on February 18th.

SpaceX Continue Starship preparations and Gains Gateway Launch Contract

Following the loss of starship prototype SN9 (see: Space Sunday: crashes, tests and an Inspiration), SpaceX has been pushing ahead with preparations for the flight of the next prototype in the series, Serial Number 10, or SN10.

Already on a launch platform at the time of SN9’s flight on February 2nd, SN10 has since been outfitted with its three Raptor engines, one of which had been previously  swapped-out from starship prototype SN8 prior to its end-of-year flight in December 2020 (see: Space Sunday: the flight of SN8 and a round-up), and which now appears to have been overhauled and declared ready for flight. The vehicle has also undergone a series of cryogenic pressure tests – filling the fuel tanks with liquid nitrogen to simulate a typical super-cold fuel load – to ensure they are fit for flight.

All of this has prompted speculation that the flight of SN10 could come within the next week – which seems a little optimistic, given that SpaceX have yet to carry out actual fuel loading tests and perform the usual static-fire engine tests. There’s also the not-so-small matter of what changes may have to be made for the “flip up” manoeuvre when a starship is supposed to raise itself to the vertical and make a tail-first landing, and whether the FAA will require a in-depth investigation and and review of both the SN8 and SN9 failures.

As a result of the SN9 test, which demonstrated only using 2 of the 3 sea-level Raptor motors to complete the flip up manoeuvre can result in a vehicle loss should one engine fail, all three will initially be fired ahead of the manoeuvre, and one immediately shut-down when the flight system confirms it has good burns on the other two. However, it remains unclear if this new arrangement is satisfactory for the FAA.

In the meantime, SpaceX has also been awarded the contract to launch the first two elements of NASA’s Lunar Orbital Platform-Gateway (LOP-G) – now  being simply referred to as the Lunar Gateway – the planned space station that will be placed in an extended halo orbit around the Moon.

The Gateway is intended to provide long-term logistical support for a permanent human presence on the Moon, although it is no longer seen as a priority for an initial US return to the lunar surface. It  is intended to provide a “way station” for crews travelling to / from the Moon, as well as eventually providing research space in its own right.

Under original planning, the Gateway would start out with just a Power and Propulsion (PPE) module and a Habitation and Logistics Outpost (HALO) module, which would be individually launched around 2024 or shortly after,  and then expanded on over time. It has now been decided that both modules should be launched together by a single vehicle, as it is felt a single launch with the two modules already mated will reduce both the technical and operational complexities in establishing the initial Gateway base.

The contract is worth US $331.8 million, and the Falcon Heavy was selected due to the performance requirements for the mission. Currently the world’s most powerful operational launch vehicle with – at the time of writing – two successful operational launches to its credit as well as its famous test flight that saw it place a Tesla car in a heliocentric orbit, the Falcon Heavy will nevertheless require some modification to launch PPE and HALO, most notably an extended payload fairing in which to house them during orbital ascent. The launch itself will take place no  earlier that May 2024.

Portrait of a Nebula

This image, from the NASA/ESA Hubble Space Telescope, features an impressive portrait of M1-63, a beautifully captured example of a bipolar planetary nebula located in the constellation of Scutum (the Shield), visible in the southern celestial hemisphere.

It is called a bipolar nebula because it has two outer lobes of gas and dust. While the exact nature of their formation is unknown, it is believed they form around binary star systems with an orbital period around one another can be measured in days. As they do so, surface material is expelled from one of the stars and the magnetic and gravitational fields of the second star disrupt the outwards flow of this material, twisting it into the distinctive lobes of the nebula, which can resemble an hourglass figure or pair of butterfly wings.

In the case of M1-63, the material being given off by one of the stars is hot and dense enough to for a brain-like centre, the two outer lobes appearing much fainter “above” and “below” it.