Category: Other Worlds and Tech

The Orion test article lifts-off from Space Launch Complex 46 at Cape Canaveral Air Force Station at the start of Ascent Abort-2, July 2nd 2019. Credit: NASA

NASA’s Orion Multi-Purpose Crew Vehicle passed a significant test on its way to its first crewed launch (due in 2022) on July 2nd, 2019, as it completed a flight test of the capsule’s launch abort system (LAS).

The LAS is a system designed to pull a crewed capsule clear of a malfunctioning rocket during an ascent to orbit, hopefully saving their lives in the process. As such, it is a significant system that must be tested and cleared for use before crewed flights can commence with a new launch vehicle.

For the Space Launch System (SLS), NASA is following its traditional approach, with the LAS designed to “pull” a crew capsule clear of launch vehicle. It does this by placing a special fairing over the capsule that has a tower extending from its top, fitted with three motors. This has always been the traditional approach to US LAS systems – by contrast, Russian LAS systems generally sit below the capsule and are design to “push” it away from a malfunctioning rocket.

The July 2nd test – called the Ascent Abort-2 (AA-2) mission – was a critical test flight, designed to test the LAS at the point in an ascent to orbit when the Orion / SLS combination will be subjected to the highest aerodynamic stresses – the so-called period of “Max-Q” – that occurs during a rapid ascent into space.

To achieve this, NASA mounted an Orion structural test article – basically an Orion capsule sans its flight systems – contained within a LAS fairing onto the motor stage of an MX Peacekeeper ICBM, and launched it into the Florida skies in a early morning ascent designed to last some 55 seconds.

In that time, the rocket was expected to reach an altitude of 9.5 kilometres (31,000 ft) and a speed of Mach 1.3, at which point the abort sequence would trigger.

As it turned out, the MX rocket motor ran “hot”, accelerating a little faster than anticipated, so reaching its assigned separation altitude 5 seconds early. Nevertheless, the abort sequence initiated correctly, and the powerful abort motors on the LAS fired, generating 181,400 kg of thrust, hauling the Orion free of the ascent motor unit.

Once a clear separation from the still ascending motor stage had been achieved, the attitude control motors at the very top of the LAS fired, flipping it and Orion over. The middle jettison motor then fired, separating the LAS from the Orion.

During an actual abort sequence, the Orion would then re-orient itself so it would be falling heat shield first, allowing its parachutes to be deployed in preparation for a splashdown. However, for the AA-2 flight, the test article did not carry a parachute system. Instead, and like the LAS, the capsule was allowed to fall back into the Atlantic, hitting it at an estimated 480 km/h (300 mph) and breaking up. Just before it did so, however, it ejected 12 bright orange data recorders not unlike those so-called “black boxes” used by aircraft. These contained critical data recorded during the 3 minute 11 second flight, and which will be assessed post-mission to confirm everything did go an planned.

That was a spectacular test we all witnessed this morning. It was really special for the programme; a really big step forward to us. It was a really great day all around – weather and the vehicle. One of the most important parts of the test was to see how the attitude control motor performed. The internal motor pressure was rock solid, straight line and it had excellent control characteristics. Everything we’ve seen so far looks great.

– Mark Kirasich, NASA’s Orion Programme Manager

The Orion test article climbs into the early morning sky over Cape Canaveral Air Force Station at the start of Ascent Abort-2, July 2nd 2019. Credit: NASA

The US has never has to use the LAS on an actual mission. However, there is no guarantee this will always be the case, and circumstances where a LAS must be used are not unkown – as the Soyuz M-10 mission in October 2018 demonstrated (see Space Sunday: of Soyuz aborts and telescopes). Therefore, passing this test was critical if  Orion and SLS are to achieve the flight goals required for NASA’s programme – Project Artemis – to return humans to the surface of the Moon.

Half-Planet, Half-Star

Discovered in 2012, GJ3470b is a “mini-Neptune” planet orbiting a red dwarf star called Gliese 3470, 100 light years from our Sun. Occupying an orbit some 6 million km (3.7 million mi – roughly one-tenth of the distance between the Sun and Mercury) from its parent, the planet has a mass of around 12.6 Earths.

None of this is particularly unusual; as I’ve noted in past Space Sunday articles, M-type stars are the most common type of star in the galaxy, and mini-Neptune type planets account for around 80% of the exoplanets discovered to date. Nevertheless, recent studies have revealed GJ3470b to be a very unique world.

The presence of an atmosphere around the planet was detected fairly soon after its discovery and prompted astronomers to take a prolonged look at it. To do this, they combined the Hubble and Spitzer space telescopes to examine the planet’s atmosphere for a total of 20 transits in front of its parent star.

These observations, using the light of the star passing through the planet’s atmosphere during the transits, allowed the astronomers to gather data on the composition of GJ3470b’s atmosphere. What was discovered came as a huge surprise.

It has been expected that the observations would reveal an atmosphere somewhat similar to Neptune’s, but such was the depth to which they could measure, it quickly became clear that GJ3470b has an almost pristine atmosphere of hydrogen and helium surrounding a large solid core.

The presence of hydrogen and helium may not sound too unusual – after all, the four gas giants of our solar system have atmospheres largely made up of those two gases. However, they also have amounts of other, heavier elements – methane, nitrogen, oxygen, ammonia, acetylene, ethane, propane, phosphine, etc., – none of which showed up in any of the spectral analyses performed by Hubble and Spitzer. This makes GJ3470b’s  atmosphere closer in nature to that of the Sun or a star than it does to a planet, leading to it being dubbed “half-planet / half-star” in some quarters, and making it the most unique exoplanet yet discovered.

Continue reading “Space Sunday: rockets, exoplanets and alien oceans” →

Two Earth-sized planets have been found orbiting a star 12.5 light-years from our own, adding to the catalogue of exoplanets located in our own cosmic back yard.

The star in question is Teegarden’s Star, a M-type red dwarf, the most common type of star in our galaxy, and therefore the most frequent type found to have planets and planetary systems. However, Teegarden’s Star is a little different to other red dwarfs we’ve observed with or without planets. For a start, despite being only a short cosmic stone’s throw from Earth, it is incredibly dim – so dim that we didn’t even notice it until 2003. Not that that in itself is usual, it’s believed that the space around us for a distance of about 20 light years could have many dim red dwarf stars hiding within it, simply because this region of our galaxy seems to have a much lower density of such stars than we see elsewhere.

What makes Teegarden’s Star odd in this respect is that it wasn’t found as a result of a search for such nearby dim red dwarfs, but because astronomers tripped over it whilst reviewing data originally gathered in the 1990s by the Near-Earth Asteroid Tracking (NEAT) project. In fact, the star is actually named for the head of the review team, Bonnard J. Teegarden, an astrophysicist at NASA‘s Goddard Space Flight Centre. The star is also somewhat unusual in that it has a large proper motion (approximately 5 arcseconds per year), marking it as one of seven stars with such large proper motions currently known.

Observations of the star made in 2010 by the Red Optical Planet Survey (ROPS) suggested the star might have at least one planet orbiting it, but the data was insufficient to draw a definitive conclusion. However, in June 2019, and after three years of verifying their data, scientists conducting the CARMENES survey at the Calar Alto Observatory announced evidence of two Earth-mass exoplanets orbiting the star within its habitable zone.

The planets were detected using the radial velocity method (aka Doppler spectroscopy), also informally referred to as the “wobble method”. Putting it simply, a star with planets doesn’t simply spin on its axis with the planets whizzing around it. Rather, the mass of the planet(s) works against the mass of the star, creating a common centre of mass which, although still inside the star, is sufficiently removed from its own centre to cause the star to effectively rolls around it (see the image on the right).

This means that when seen from Earth, there are times when the star can seem as if it is moving “away” from our telescopes, signified by its light shifting to the red end of the spectrum. Equally, there are other times when it appears to be moving “towards” us, signified by its light shifting to the blue end of the spectrum. It is by observing and measuring this visible Doppler shift that tells us there are planets present. In all, this method of stellar observation has accounted for almost one-third of all exoplanets found to date.

The key point with this method of observation is not only does it allow astronomers to locate planets orbiting other stars, it actually allows maths to be applied, allowing the number of potential planets to be discerned, their distance from their parent star and important factors such as their probable mass, which in turn allows their likely size and composition to be estimated.

In the case of Teegarden’s Star, the data indicates the two planets orbiting the star – called Teegarden’s b and Teegarden’s c respectively – have a mass of around 1.05 and 1.1 that of Earth each, suggesting they are probably around the same size as one another and comparable to Earth in size. Teegarden’s b, the innermost planet, orbits its parent every 4.9 terrestrial days, and Teegarden’s c every 11.4 terrestrial days.

The combined mass of these planets, coupled with the amount of Doppler shift exhibited by Teegarden’s Star has led to some speculation there may be other, larger planets orbiting much further out from the star. Such planets would be hard to locate because Teegarden’s Star is so dim when observed from Earth, astronomers cannot rely on the transit method  – where large planets passing in front of their parent star can cause regular dips in its apparent brightness – to identify their existence.

However, what is particularly interesting about Teegarden’s b and c is their location relative to their parent, and the nature of Teegarden’s Star itself. The latter is a particularly cool and low-mass red dwarf, with just one-tenth of the Sun’s mass and a surface temperature of 2,700°C (4890°F). This means that at their respective distances, both planets are within the star’s habitable zone – and may well have atmospheres.

The two planets resemble the inner planets of our solar system. They are only slightly heavier than Earth and are located in the so-called habitable zone, where water can be present in liquid form.

– Mathias Zechmeister, University of Göttingen, Teegarden planetary team lead

This latter point  – the existence of atmospheres around both planets – has yet to be proven. As noted previously in these articles, M-type stars are actually not nice places; when active (and Teegarden does seem to be well past its active stage) in their youth, they can be prone to violent irradiative outbursts which could both strip away the atmospheres of any planets orbiting them over time and irradiate the planets’ surfaces. And even if  the planets do have atmospheres, their close proximity to their parent likely means they are both tidally locked with their same face towards it. This is liable to make them pretty inhospitable places and potentially prone to extremes of weather.

But there is one other interesting point to note here. While Teegarden’s Star may well be dim to the point of being practically invisible when viewed from Earth, the same isn’t true the other way around: our Sun would be a bright star in the skies over Teegarden’s b and c. What’s more, the angle of our solar system to those worlds (practically edge-on) means that if we were to imagine one of them having an intelligent, scientific race, they could easily detect the planets orbiting our Sun using the transit method of observation, and could probably deduce up to three of the innermost planets might be capable of supporting life.

Continue reading “Space Sunday: alien worlds, telescopes and lightsails” →

Once regarded as a planet that may harbour life, Venus – as we know it today – is a hellish place. Cursed with a runaway greenhouse effect, the surface temperatures (averaging 735 Kelvin or 462°C / 863°F) are hot enough to melt lead and mark it was the hottest planetary body in the solar system. The atmosphere is both a toxic cauldron so dense that it exerts a surface pressure 92 times greater than our own – the equivalent of being 900 m (3,000 ft) under water on Earth.

Venus is also unusual in other ways: it has a retrograde rotation (it spins on its axis in the opposite direction to Earth and most of the other planets), and it takes 243 terrestrial days to complete one rotation but only takes 224.7 days to complete an orbit of the Sun, making a “day” on Venus longer than a year.

Despite its hostile conditions, it has long been believed that Venus was at one time in its ancient past a far more hospitable world, potentially warm a wet, and spinning a lot faster on its axis (quite possibly in the same direction as the Earth spins). However, at some point  – so the accepted theories go – Venus experienced a massive impact, one sufficient enough to slow – and even reverse – its rotation and which also left it the broiling, hostile world we know today.

However, a new study involving the University of Bangor, Wales, the University of Washington and NASA, suggests not only did Venus once had a liquid water ocean, but that ocean may have actually been the catalyst that brought about the planet’s dramatic change.

To put it simply, tides act as a brake on a planet’s rotation because of the friction generated between tidal currents and the sea floor. On Earth, this results in the length of a day being shortened by about 20 seconds every million years. Given this. the team responsible for the  study investigated how such interactions might impact Venus. Using a numerical tidal model, the accepted belief that Venus once had a world-girdling ocean, and applying it to planetary rotational periods ranging from 243 to 64 sidereal Earth days, they calculated the tidal dissipation rates and associated tidal torque that would result from each variation in ocean depth and rotational period. Their work revealed that ocean tides on Venus would likely have been enough to slow the planet’s rotation it down by up to 72 terrestrial days every million years.

This might not sound a lot, but of the course of around 10-50 million years, it would have been enough to slow Venus’s rotation and bring it to how we see it today. In turn, this slowing of rotation would have accelerated the evaporation of an ocean waters on the sunward facing side of the planet, both increasing the atmospheric density and trapping more heat within the atmosphere, accelerating the planet’s greenhouse effect, in turn increasing the rate of ocean evaporation in what would have been a closed cycle. Add to that the planet’s known volcanism, and the team estimate that it would have taken around 100-120 million years to turn Venus into the planet we see today.

This work shows how important tides can be to remodel the rotation of a planet, even if that ocean only exists for a few 100 million years, and how key the tides are for making a planet habitable.

– study co-lead Dr. Mattias Green, University of Bangor

The study findings have potentially important implications for the study of extra solar planets, where many “Venus-like” worlds have already been found. From this work, astronomers have a model that could be applied to exoplanets located near the inner edge of their circumstellar habitable zones, helping to determine whether they might have at some point potentially have had liquid water oceans, and how those oceans may have affected their development.

Fly Your Name to Mars

Mid July through August 2020 will see NASA’s next rover mission launched to Mars, and as with a lot of their recent exploratory missions, NASA is giving members of the public the opportunity to have their names flown with the vehicle.

Between now and September 30th, 2019, NASA is inviting one million members of the public to submit their names and postal codes to Send Your Name (Mars 2020). These names will then be laser-etched onto a little chip roughly the size of a penny that will be mounted on the rover and carried to Mars. In return, successful applicants obtain a “boarding pass” similar to the one shown below, indicating their name will be flown on the mission.

The Mars 2020 rover is based on the same chassis and power system as used by the Mars Science Laboratory Curiosity rover. It will also use the same type of landing system, featuring a rocket-powered “skycrane” that will hover a few metres above the surface of Mars and then winch the rover down to the surface. However – and for the first time in the history of planetary exploration – Mars 2020 will have the ability to accurately re-target its landing point prior to committing to lower the rover, thus allowing it to avoid last-minute obstructions that might otherwise damage the rover or put it at risk.

Core to this capability is a instrument called the Lander Vision System (LVS), which has been undergoing tests in California’s Death Valley attached to a helicopter. LVS is designed to gather data on the terrain the lander is descending towards, analyse it to identify potential hazards and then feed the information to a guidance system called Terrain-Relative Navigation (TRN), which can then steer the landing system away from hazards, allowing the skycrane to winch the rover to the ground in a (hopefully) a safe location.

Mars 2020 is due to be launched between July 17th and August 5th 2020 to arrive on Mars at Jezero Crater on February 18th, 2021.

Continue reading “Space Sunday: Venus, Pluto, and a mini round-up” →