Tag: Astronomy

After a two-day delay, NASA’s Transiting Exoplanet Survey Satellite (TESS) launched from Cape Canaveral Air Force  Station atop a SpaceX Falcon 9 booster on Wednesday, April 18th.

As I previewed in my previous Space Sunday report, TESS is designed to seek out exoplanets using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope. Once in its assigned orbit and operational, TESS will work alongside the Kepler space observatory – now sadly nearing the end of its operational life, and eventually the James Webb Space Telescope – in seeking worlds beyond our own solar system.

It will be another 56 days before TESS has reached its unique orbit, a “2:1 lunar resonant orbit“, which will allow the craft to remain balanced within the gravitational effects of the Moon and Earth, thus providing a stable orbital regime which should last for decades. However, the launch was perfect after issues with the Falcon 9’s navigation systems prompted the initial launch attempt on Monday, April 16th. Once it had lifted the upper stage and its tiny payload – TESS is just 365 kg in mass and about the size of an upright fridge / freezer combination – the Falcon 9’s first stage completed a successful burn back manoeuvre and made a successful at-sea landing on the SpaceX Autonomous Drone Ship Of Course I Still Love You, waiting some 300 kilometres off the Florida coast.

The second stage of the rocket placed TESS into an initial 250 km circular orbit about the Earth before shutting its motor down for a 35-minute cruise period which correctly positioned the vehicle to allow the engine to be re-lit and send TESS on its way towards a 273,000 km apogee orbit. Over  the next several weeks, the instruments aboard TESS will be powered-up and calibrated, including the four cameras it will use to imaged the stars around us in an attempt to locate planets orbiting them.

The first exoplanet – the ” hot Jupiter” 51 Pegasi B, unofficially dubbed Bellerophon, later named Dimidium and some 50 light years away –  was discovered in 1995. In the 23 years since that event, some 3,708 confirmed planets (at the time of writing) have been found, with a list of several thousand more awaiting verification. Most of these have been discovered by using the transit method, with the vast majority by the Kepler space observatory. Such are the capabilities of TESS, it could double this count during its whole-sky survey, the first phase of which will last two years.

TESS’s primary mission is scheduled to last two years – but it orbit means it could study the skies around us for decades, seeking out planets amount the 200,000 stars that are the nearest to us.

SpaceX: Party Balloons and Bouncy Castles?

Elon Musk loves to tease. He’s also generally in earnest when discussion space flight. Sometimes the two things combine in unusual ways. Take a trio of tweets he sent on April 16th, 2018, for example:

This is gonna sound crazy, but … SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon. And then land on a bouncy house.

Elon Musk’s trio of tweets, April 16th, 2018

Precisely what he meant has been the subject of much Twitter debate and theorising in various space-related blogs, but the CEO of SpaceX is now keeping mum on the subject; most likely enjoying the feedback and making plans.

SpaceX has serious ambitions to make their launch vehicles pretty much fully reusable. As we already know, the company has pretty much perfected the successful landing, refurbishment and re-use of Falcon 9 first stages (also used in triplicate on their Falcon Heavy booster), and plan to use the same approach with their upcoming BFR – standing for Big Falcon (or at least, a word that sounds close to “Falcon” but with a cruder meaning) Rocket – formerly, the Interplanetary Transport System.

To date, SpaceX has successfully recovered 24 Falcon 9 first stages, with almost half of those recovered now refurbished and either re-flown, or awaiting re-use. But the first stage – which does all the heavy lifting, is perhaps the “easiest” element of the vehicle to recover. It does not achieve orbital velocity (around 7,820 metres per second, or 17,500 mph), but instead tends to reach a peak velocity of around 1,716 metres per second (roughly 3,800 mph or Mach 5).

While this is still enough to generate a significant amount of heat and cause a first stage to break-up / burn-up in an uncontrolled descent, it is “slow” enough to avoid the need for extensive (and heavy) shielding to protect against the friction heat of passage back into the denser part of Earth’s atmosphere, providing the stage can be oriented correctly so three out of its set of nine motors can be re-lit. The exhaust plume from these forces the atmospheric compression generated by the rocket’s penetration of the upper layers of the denser part of the atmosphere (and which actually generates the associated re-entry heat), to occur away from the rocket, so the need for additional heat shielding is avoided.

However. recovering the upper stage of the rocket is altogether a different proposition. This does reach orbital velocity, and so finding a way in which it can be safely recovered without relying on expensive and heavy heat shielding which would both increase launch costs and reduce the payload carrying capabilities of both the Falcon 9 and the Falcon Heavy is a doozy of a problem. So much so, that SpaceX have twice cancelled attempts to make the rocket’s upper stage recoverable – and as recently as late 2017, it was believed further attempts at trying to get the stage to a point where it could be recoverable had been abandoned in favour of focusing on the BFR’s massive upper space ship stage – which as a crew / passenger carrying vehicle needs to be able to make safe landings.

So what do Musk’s tweets mean? how could a balloon be used to slow a vehicle and help it through the searing heat of orbital re-entry (where the heat load is around 27 times hotter than the heat experienced by the first stage)? The most likely explanation is that SpaceX are exploring the potential of using a ballute – a portmanteau of balloon and parachute – with the upper stage.

Continue reading “Space Sunday: SpaceX – balloons, bouncy castles and rockets” →

On Monday, April 16th, 2018, after being delayed from a planned December 2017 lift-off, the launch window opens for NASA’s Transiting Exoplanet Survey Satellite (TESS).

As its name implies, TESS is designed to seek out exoplanets using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope. Once in its assigned orbit and operational, TESS will work alongside the Kepler space observatory – now sadly nearing the end of its operational life and eventually the James Webb Space Telescope – in seeking worlds beyond our own solar system.

Roughly the size of an upright ridge/freezer combination, the 356 kg (800 lb) TESS is due to be launched on its way atop a SpaceX Falcon 9 booster from Launch Complex 40 at Canaveral Air Force Station, Florida, on April 16th, 2018, in a launch window that opens at 18:32  EDT (22:32 UT).  The rocket – sans it’s payload – underwent a static rocket motor test on Wednesday, April 9th, prior to it being returned to the launch preparation facility, where the Payload system and fairings containing TESS were mated to it in readiness for the launch. As well as launching TESS, SpaceX plan to recover the Falcon 9’s first stage.

Once on its way, Tess will take 60 days to reach its unique orbit, a “2:1 lunar resonant orbit“, which will allow the craft to remain balanced within the gravitational effects of the Moon and Earth, thus providing a stable orbital regime which should last for decades. In addition, the orbit means that TESS will be able to survey both the northern and southern hemispheres.

During this initial 60-period, scientists and engineers will spend the first week re-establishing contact with TESS and confirming its operational status as its instruments are cameras are powered-up. The instruments will then go through an extended commissioning and calibration phase, as engineers monitor the satellite’s trajectory and performance. After that, TESS will begin to collect and downlink images of the sky.

While Kepler has so far found the most exoplanets in our galaxy, it has done so by surveying relatively small arcs of the space visible to it. TESS, however, will do things differently. It will scan the galaxy in hundreds of light-years in all directions, a sphere of space containing some 20 million stars, paying particular attention to the brightest stars around us in the hope of detecting planetary bodies in orbiting them.

This will be achieved by dividing space into 26 individual “tiles”, allowing the four imaging systems on the craft to repeatedly observe a “strip” of four tiles at a time for a minimum of 27 days each (and parts of some for up to a year at a time) before moving to the next strip, working its way around the sky. In this way, it is estimated TESS will be able to survey up to 200,000 stars in both the northern and southern hemispheres over multiple years.

Amid this extrasolar bounty, the TESS science team aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth. Many of TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterize atmospheric conditions, and even look for signs of habitability.

In this latter regard, TESS will pave the way for detailed studies of candidate exoplanets by the James Webb Space Telescope (JWST), now scheduled for launch in 2020. While TESS cannot look for atmospheric or other signs of life on the distant worlds it locates, JWST will be able to do just that. So, even as we prepare to say a sad goodbye to Kepler, the hunt of exoplanets is actually just hotting up.

Continue reading “Space Sunday: of exoplanets and naming Charon’s features” →

China’s first orbital laboratory, Tiangong-1 (“Celestial Palace 1”) is due to re-enter the Earth’s atmosphere within the next 24 hours.

Launched in 2011, the 10.4-metre-long (34-foot) unit weighing 8.5 tonnes, was the first phase in China’s project to gain experience in Earth-orbit operations in order to establish a space station in the 2020s. It  operated for four-and-a-half-years, and was visited by two crewed missions before operations were officially brought to a close in 2016, following the launch of the Tiangong-2 orbital module.

Originally, it had been anticipated that Tiangong-1 would be de-orbited and allowed to burn-up in the upper atmosphere in late 2017. However, it was also claimed that the Chinese had lost attitude control over the unit, and that it would de-orbit some time in March 2018. These claims that control had been lost – strongly denied by the Chinese, led to over-the-top reports that the Earth was in imminent danger of the station forming a fireball and crashing to the ground within a city.

While it is true that the unit could re-enter the atmosphere anywhere between 43-degrees north and 43-degrees south, the fact is that much of the laboratory’s orbit takes it over open sea, so the risk than any part of it which might survive re-entry and disintegration in the upper atmosphere could strike a populated centre is considered low.

At the time of writing, orbital tracking suggested that Tiangong-1 will re-enter the denser part of Earth’s atmosphere and start to break-up no earlier than 00:18 UTC on Monday, April, 2nd, 2018 (roughly 17:18 EST) +/- 1.7 hours.  As Tiangong-1 descends into the atmosphere it will be subject to frictional heat and vibration which will combine to start breaking it apart. As this happens, it is liable it will start tumbling, speeding the process of disintegration and encouraging more of it to burn-up due to frictional heat. The hope is that almost nothing of the station will survive this burn-up process to actually reach the surface of the planet.

But even if some do, again, the chances of them hitting a populated area and causing a loss of life appear somewhat remote. In this, Tiangong-1 reflects the US Skylab mission in 1979 and the Russian Salyut 7 / Cosmos 1686 combination of 1991. Both of these where much larger than Tiangong 1 (77 tonnes and 40 tonnes respectively), and made uncontrolled re-entries into Earth’s atmosphere. In both cases, wreckage did not cause loss of life. It’s also worth pointing out that something equal to, or approaching, the size and mass of Tiangong-1 re-enters Earth’s atmosphere approximately every 3 or 4 years – all without harm to those below.

Those interested in tracking the laboratory’s orbit in real-time can do so via Aerospace Corporation’s Tiangong-1 re-entry dashboard .

The Moon: Gateway or Direct?

As NASA considers whether or not to acquire more than one propulsion module for the proposed Lunar Orbital Platform-Gateway (LOP-G, previously known as the Deep Space Gateway), more are adding their voices to concern that NASA’s idea of establishing a human presence on the Moon’s surface by way of an orbital facility is not the most ideal way to go.

The LOP-G has taken various forms over the course of the last several years. envisaged as a small space station occupying a near-rectilinear halo orbit (NRHO) around the Moon, it was previously known as the Deep Space Gateway, intended to support the (now-cancelled) Asteroid Redirect Mission. It was then seen as a means of supporting lunar missions and – eventually – missions to Mars. The reasons for the station have always been pretty thin, and in an Op-Ed written for Spacenews.com, Robert Zubrin offers an alternative approach to a return to the Moon which forgoes the need for LOP-G.

Zubrin, along with David Baker, is the author of  Mars Direct, a proposal for establishing a human presence on Mars. It was conceived in the 1990s in response to NASA’s Space Exploration Initiative of 1989. Also called the 90-Day Report, this sought to set-out a roadmap for reaching Mars. This involved developing orbital facilities around Earth which would in turn allow for a return to the Moon, where large-scale facilities could be built from which humans could embark on missions to Mars. With a 30-year time frame and an estimated cost of US $450 billion, it was a plan built on the specious idea that the Moon offered the “easiest” route to reaching Mars, and which ultimately went nowhere.

Mars Direct, on the other hand, presented the means to reach Mars with an initial human mission in just 10 years from inception, and at a cost of some US $30 billion overall. This included all the development costs of the launch vehicle and the required crew infrastructure which, once developed, could be used to undertake subsequent missions (launched every 2 years, to take advantage of Earth’s and Mars’ orbits) at a cost of US $1 billion a year. The mission profile also provided the means to use local resources on Mars to reduce overheads (such as using the Martian atmosphere to produce fuel stocks) and establish a permanent presence on the planet, as well as offering crews an assurance of getting back to Earth if anything went wrong with a particular mission.

Continue reading “Space Sunday: Tiangong-1’s return and going to the Moon” →