Space Sunday: of rockets and planets

SpaceX Crew Dragon (l) and the Boeing CST-100 Starliner: Further delays could threaten US access to the ISS. Credit: SpaceX / Boeing

The first SpaceX Crew Dragon (aka Dragon 2) vehicle destined to fly in space has arrived in Florida ahead of its launch, due in August 2018. The capsule is intended to be part of an uncrewed first flight to test the vehicle’s flight test systems.

Prior its transfer to Kennedy Space Centre (KSC), the capsule and service module were the subject of extensive thermal vacuum chamber tests at NASA’s Plum Brook Station in Ohio. The world’s only facility capable of testing full-scale upper-stage launch vehicles and rocket engines under simulated high-altitude conditions, the chamber is a vital part of pre-launch testing – although by the date of the capsule’s arrival at KSC, the results of the Ohio testing had not been made public.

SpaceX’s first Crew Dragon spacecraft is prepared to undergo testing at the In-Space Propulsion Facility of NASA’s Plum Brook Station in Sandusky, Ohio on June 13th, 2018. Credit: SpaceX

No official date for the first Crew Dragon flight has been released, but SpaceX are pushing ahead with work to prepare the vehicle for launch, in anticipation of the flight being given the green light for August. The test flight should see the uncrewed test vehicle fly to the International Space Station (ISS), with a follow-up 14-day crewed test flight due to take place in late 2018 / early 2019.

The arrival of the Crew Dragon test article at KSC came at the same time as a further US government report raised concerns about both SpaceX and Boeing – the other company contracted to make crewed flights to / from the ISS using their CST-100 Starliner capsule – being able to meet the current schedule for commencing formal operations.

A July 11th, 2018, report from the independent Government Accountability Office (GAO) points out that if any significant issues arise with either / both vehicles prior to their formal certification, it could see one or other or both companies being unable to commence active crew launches within the anticipated time frames specified by NASA. Were this to be the case, America would effectively be without the means to send astronauts to the Space Station, as the current contract to fly US crew aboard Russian Soyuz vehicles expires in November 2019.

Under the original schedule, the Boeing CST-100 was to have been certified for crew operations in January 2019, and the Crew Dragon in February 2019. However, both these dates were recently revised: the CST-100 certification slipping to December 2019 and Crew Dragon’s to February 2020.

With crew rotations to the ISS lasting 6 months, this slippage – which moved the first official crewed flights of both CST-100 and Crew Dragon to several months after the Soyuz contract ends – were not seen as a significant issue. However, the GAO report warns that certification of both vehicles could slip to around August 2020 should difficulties with either / both vehicles be encountered as a result of the test flights (or other reasons). This would potentially see a nine-month gap open between the last of the planned US Soyuz flights and a commencement of CST-100 / Crew Dragon flights, more than the span of a crew rotation, with no contingency currently in place to allow continued US access to the ISS until either of the new vehicles is ready to fly.

A “Temperate” Exoplanet?

Ross 128 is a red dwarf star just 11 light-years away from our Sun that over the years has been a source of interest for astronomers. First catalogued in 1926, the star is too faint to be seen with the naked eye, but is classified an old disk star with a low abundance of elements other than hydrogen and helium. Like most red dwarf stars, Ross 128 is given to violent flare activity, although its extreme age makes such events a lot less frequent than “younger” red dwarfs.

In mid-2017, Ross 128 caused something of a stir when a mysterious burst of signals was recorded apparently coming from its general vicinity. Dubbed the “Weird!” signals, the series of unusual “transmissions” were received by the  Arecibo radio telescope, Puerto Rico on May 12th/13th, 2017.

The 2017 Weird! signal that seemed to come from Ross 128 (but has never been re-acquired). Credit: UPR Aricebo

At the time, the signals caused a lot of excitement and talk of “aliens” being involved – although no planets had actually been detected around Ross 128. As I reported in July 2017, after further study, it was determined that the most likely explanation for the signals was that they’d been accidentally picked up from satellites occupying the same part of the sky as Ross 128 at the time Aricebo happened to be listening; all attempts to re-acquire them by numerous radio telescoped failed to do so.

While there is no reason to change the view that the odd signals of May 2017 were from local satellites rather than originating with Ross 128, in November 2017 it was confirmed the star does in fact have a planet orbiting it.

Referred to as Ross 128 b, the planet was first detected in July 2017 by a team operating the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the La Silla Observatory in Chile. However, it was not until November of 2017 that the astronomers were able to confirm that had located the planet.  Since then, the planet has been the subject of indirect scrutiny to try to better determine its characteristics, and the results are interesting.

The HARPS data initially suggested the planet to be roughly around the size of Earth and orbiting in the star’s habitable zone. However, further characterisation of the planet – including whether or not it has an atmosphere – has been hampered by the fact that its orbit around its parent star means it doesn’t actually transit between Ross 128 and Earth.

An artist’s impression of Ross 128 b orbiting its parent star. Credit: ESO/M. Kornmesser

As this presents a barrier to analysing the planet directly by the effect it and its atmosphere (if it has one) has on light coming from its parent star, astronomers instead turned to studying Ross 128 itself in their attempts to better understand the potential nature of Ross 128 b.  In particular, a team led by Diogo Souto of Brazil’s Observatório Nacional used Sloan Digital Sky Survey‘s APOGEE spectroscopic instrument to measure the star’s near-infrared light to derive abundances of carbon, oxygen, magnesium, aluminium, potassium, calcium, titanium, and iron.

As noted above, when stars are young, they are surrounded by a disk of rotating gas and dust from which rocky planets accrete. The star’s chemistry can influence the contents of this disk, and in turn affect a planet’s mineralogy and interior structure. For example, the amount of magnesium, iron, and silicon in a planet will control the mass ratio of its internal core and mantle layers. So by studying a star, it is possible to determine the likely composition of a planet orbiting it.

The team’s studies revealed Ross 128 has iron levels similar to our Sun, and while they were unable to measure its abundance of silicon, the ratio of iron to magnesium in the star indicates that the core of Ross 128 b should be larger than Earth’s., with the planet likely being around 1.3 to 1.7 times bigger than Earth. The observations also determined that temperatures at or near the “surface” of the star are around 3,000 C (5,400 F). The researchers used this information, along with Ross 128 b’s orbital radius and likely distance from the star, to figure out how much stellar energy the planet receives – and, therefore, how hot it is likely to be.

The result? Ross 128 b probably has an “equilibrium temperature” of about 21 C (70 F), which sounds quite balmy, and initially marks the planet as possibly “temperate”. However, the estimate comes with a caveat: a planet’s temperature depends greatly on the composition and thickness of its atmosphere. Until such time as something like the James Webb Telescope (JWST) can study the planet directly, the nature of Ross 128 b’s atmosphere remains a complete mystery, so it is far too early to assess anything about the planet’s potential habitability.

NASA Adds to SLS Block 1 Launches

NASA has added further launches to the Space Launch System (SLS) Block 1 manifest, and is seeking to procure additional upper stages for the vehicle and certify them for human launches.

An artist’s impression of a Space Launch System / Orion combination lifting off from Kennedy Space Centre’s Pad 39B. It’s now expected the Block 1 vehicle will be flown at least 3 times, rather than just once. Credit: NASA

Originally, the Block 1 vehicle was only due to fly once before being replaced by the more powerful Block 1B vehicle, which uses a different upper stage called the Exploration Upper Stage, intended for deep space missions. However, with Congress agreeing to fund the construction of a second mobile launcher platform for SLS,  NASA has opted to employ the first of the mobile launch platforms specifically for Block 1 vehicle launches, and then switch to using the Block 1B vehicle when the second mobile launcher platform is introduced.

This means that the planned Exploration Mission 2 (EM-2) flight, which will feature the first crewed flight of the Orion capsule system, will now be atop a Block 1 launch vehicle,. This launch is currently scheduled for June 2022. In addition, a “cargo” launch of the SLS Block 1 has also been scheduled for 2022, possibly ahead of EM-2. It is believed this launch might be for the Europa Clipper mission that will study Jupiter’s moon Europa from an orbit around the planet, however, NASA has not confirmed this – Europa Clipper having been targeted for a 2025 launch.

The first SLS Mobile Launcher platform is in fact a conversion / enhancement of the MLP originally intended for the cancelled Ares 1 launch system. The unit is seen here at Kennedy Space Centre, with one of the tracked crawler transporter vehicles that piggyback the MLP and stacked rocket from the Vehicle Assembly Building at KSC to the launch pad. Credit: NASA

It is possible the “cargo” mission and EM-2 could yet be swapped so EM-2 goes ahead first. This depends on what happens with the Block 1 vehicle’s upper stage. Called the Interim Cryogenic Propulsion Stage (ICPS), it is based on a Delta 4 upper stage, which is not intended for use in crewed launches. So in order for the EM-2 mission to go ahead using a Block 1 SLS, the ICPS must undergo proper certification for crewed launches.

In the meantime, the initial uncrewed launch of a Block 1 SLS vehicle, which will see the Orion vehicle fly in space for the second time, remains scheduled for the end of 2019. However, NASA has acknowledged that the development programme to get the vehicle ready for launch still faces “four to six months of risk”, meaning it could still slip into 2020.

What Clobbered Uranus?

Uranus is one of the bigger  – literally as a well as figuratively – enigmas of the solar system. Known to have thermal anomalies and a magnetic field that is off-centre, the planet’s biggest enigma is that is effectively rolling around the Sun on its side, having an axial tilt of 98°. Thus; it has radical seasons and a day-night cycle at the poles where a single day and night last 42 years each.

It’s long been suspected that Uranus was given its odd tilt as a result of a collision with another body early in the history of the solar system – but just what was the size of that body? Why did the collision not rip Uranus’ atmosphere away? Could the planet’s off-centre magnetic field and thermal anomalies be linked to its odd tilt, and if so, how?

The interior structure of Uranus: the core is thought to have “lopsided” masses of rock and material within it, giving the planet its off-centre magnetic field, which the icy mantle is thought to be surrounded by a thin shell of material left over from the impact with the body that “tipped” the planet over, which reflects any heat generated within the planet inwards, rather than allowing it to be fully transferred to the surrounding atmosphere. Credit: A Francesco / SF Wolfman

Researchers from the University of Durham, UK, believe they have the answers to all of these questions. Using a technique called smoothed particle hydrodynamics (SPH) simulations, they ran over fifty different scenarios using bodies of different compositions, masses and sizes to try to recreate the situation we see with Uranus today. Analysis of the simulations showed that the most likely culprit was a protoplanet around 2 or 3 times the mass of the Earth which caught Uranus a “glancing” blow around 4 billion years ago, very early in the solar system’s history.

This collision was likely enough to both topple Uranus onto its side and destroy the impacting body  – but not enough to tear the planet’s atmosphere away. The simulations also showed that debris from the collision likely did three things. Firstly, it provided the material needed to form Uranus’ inner moons and give rise to its ring system. Secondly, some material from the collision likely formed molten lumps of ice and rock which fell into the planet’s core, forming off-centre masses within it and causing the planet’s off-centre magnetic field. Finally, the simulations revels that some of this debris likely formed a thin shell around the planet’s mantle of water, ammonia and methane ices, which traps internal heat while leaving the surrounding atmosphere extremely cold as a result of it receiving little thermal energy from within the planet.

The team’s work, which has been subjected to study by other institutions, is considered to be the most comprehensive explanation to date for Uranus’ oddities, and a possible blueprint for what we might find among some of the larger exoplanets the JWST will hopefully be able to study in the near future.

 

Advertisements

Have any thoughts?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.