Category: Other Worlds and Tech

NASA has confirmed the first flight of the Orion / Space Launch System (SLS) will not include a crew. As I recently reported, the US space agency had been considering shifting gear with with the new combination of launch vehicle and the Orion Multi-Purpose Crew Vehicle to include a crew on the maiden flight, referred to as Exploration Mission 1 (EM-1). The change in direction was prompted by a request from the Trump administration to acting NASA Administrator Richard Lightfoot, in an attempt to accelerate the human space flight programme.

On Friday, May 12th, Lightfoot indicated that while it would be technically feasible to make EM-1 a crewed mission, the agency would not do so on the grounds of costs. For an uncrewed flight, the Orion vehicle does not need to be equipped the life support, flight control and other additional systems a crew would need. would require. Doing so would require an additional expenditure of between US $600 and $900 million  – costs which would otherwise be deferred across several years in the run-up to the originally planned crewed launch for Orion / SLS – called EM-2, slated for 2021. However, EM-1 will still be delayed until mid-2019.

The reasons for the EM-1 delay are due to unrelated issues with various parts of the Orion / SLS programme. Again, as covered in recent Space Sunday updates, the European-built Service Module, which will provide the Orion capsule with power, consumables and propulsion, is running behind schedule. In addition, the programme is also experiencing delays in developing key software.

These issues mean that pushing back the EM-1 launch was fairly inevitable. Had NASA been able to comfortably combine equipping the Orion vehicle for a crewed launch in 2019, then it would have roughly coincided with the 50th anniversary the first human lunar landing by NASA astronauts Neil Armstrong and Buzz Aldrin during the Apollo 11 mission in July 1969.  Instead, NASA will continue implementing the current baseline plan, with the second Orion / SLS flight carrying a crew into space. However, this mission may also be pushed back beyond 2021.

Saturn’s Hexagon to Star in Cassini’s Finale

As I’ve been covering, the joint NASA-ESA Cassini mission to Saturn is now in its last phase, as the spacecraft makes a final series of 22 orbits around the planet, diving between Saturn’s cloud tops and its rings in the process.

However, in addition to exploring a region of space no other mission has properly examined, Cassini’s final series of orbits around Saturn provide an unprecedented opportunity to study the massive hexagonal storm occupying the atmosphere of the planet’s northern polar region.

First seen by the Voyager missions which flew by Saturn in 1980 and 1981 respectively, the storm is of a massive size – each side of the hexagon measures around 13,800km (8,600 mi), greater than the diameter of Earth.; it rotates at what is thought to be the speed of the planet’s interior: once every 10 hours 39 minutes. However, due to Saturn’s distance from the Sun (an average of 9.5549 AU) and its axial tilt (26.73°), the northern polar region only gets about 1% as much sunlight as Earth does; making steady observations of the storm difficult. Cassini’s final series of orbits, passing as they do over Saturn’s north pole offers a unique opportunity to examine the storm in some detail.

During the first passage between Saturn and its rings on April 26th, Cassini captured a string of black-and-white images of the region, include the vortex at the centre of the storm, which were subsequently stitched together into a short movie (above).

The passes over Saturn during these final orbits should allow Cassini to use its wide-angle camera to gather detailed images of the storm whenever possible, which may in turn help scientists probe its secrets – including what is powering it, and why it has such a clearly defined boundary between itself and Saturn’s atmosphere at lower latitudes.

Cassini has already completed two “ring dives”, with the third scheduled pass occurring on Monday, May 15th. The mission as a whole will end on September 15th, when the vehicle will enter the upper reaches of Saturn’s atmosphere and burn-up.

Continue reading “Space Sunday: launches, storms, simulations, and space walks” →

NASA’s Cassini mission has completed the first of its final 22 “dives” through the gap between  Saturn its ring system. In the process, the craft came to its closest past so far over the planet’s cloud tops.

As I noted in my previous Space Sunday update, after 20 years in service and with manoeuvring fuel running out, the mission is set to end on September 15th, 2017, when the veteran spacecraft will enter the upper reaches of Saturn’s atmosphere and burn up, preventing any risk of the vehicle colliding with one of Saturn’s moons and risk contaminating it with the radiation from its plutonium power cells.

This first pass between planet and rings was a complete dive into the unknown – so much so, that the spacecraft was out of contact for 20 hours during the critical part of the pass. This was because prior to making the pass, the vehicle had to be oriented so that its 4-metre (13 ft) diameter communications dish was facing away from Earth and into the direction of flight, so it could act as a shield to prevent any dust particles within gap impacting more sensitive parts of the vehicle.

NASA’s Deep Space Communications network lost contact with the vehicle at 09:00 UT, on April 26th, as Cassini cross Saturn’s ring plane. The signal was successfully re-acquired at 06:56 UT on April 27th, after the vehicle had cleared the gap and could re-orient itself and point its communications dish back towards Earth. The transfer of data gathered during the pass commenced a few minutes later.

“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Cassini Project Manager Earl Maize at NASA’s Jet Propulsion Laboratory, California, as the data from the spacecraft started flowing. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

The gap between the rings and the top of Saturn’s atmosphere is about 2,000 km (1500 mi) wide, and Cassini came within 3,000 km (1900 mi) of Saturn’s cloud tops, in an area where there was a risk of smoke particle sized motes of dust being encountered. Small as they might be, the fact that the probe was travelling at some 124,000 km/h (77,000 mph) relative to Saturn meant that any dust striking an unprotected part of the vehicle could have been catastrophic, hence using the communications antenna (which could suffer some damage without serve loss of capability) as a shield.

“In the grandest tradition of exploration, NASA’s Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare,” said Jim Green, director of the Planetary Science Division at NASA Headquarters.

The data from Cassini is already being analysed and revealing more about Saturn and it’s atmosphere, but it has been the images that were released following the pass which have stunned observers on Social media – although some needed to have their perspective adjusted as the first of the raw images appeared.

“Hey, it’s a GIF of something you think’s gonna be cool, but it’s Cassini proving it’s no better at camera s*** than somebody getting shot at,” one commentator chose to Tweet. This prompted a quick response from fellow space enthusiast, Jason Major (whose images are used in this article); “Cute. Now realise Cassini is taking these pics w/a camera built in 1996 while travelling 65,000 mph where sunlight is 100x dimmer than here.”

Cassini’s second ring-dive will occur on Tuesday, May 2nd.

Continue reading “Space Sunday: Saturn, spacesuits and printing a base on the Moon” →

NASA’s Cassini spacecraft performed what is effectively its last close flyby of Titan, Saturn’s largest moon on Saturday, April 22nd, 2017, marking a final opportunity for the mission to make up-close observations of the lakes and seas of liquid hydrocarbons that spread across the moon’s northern polar region and for the probe to use its radar imager pierce the haze enveloping the moon and map its surface. The next time the spacecraft passes Titan, it will be on its way to its destruction.

It is twenty years since the mission was launched from Earth, a combined NASA / ESA attempt to explore Saturnian system and probe the mysteries of Titan. It took seven years for the vehicle, carrying the European Huygens Titan Lander to is own rendezvous with the surface of Titan. Over the last thirteen years, the Cassini vehicle, roughly the size of a small truck and massing (at launch), 5 tonnes, has revolutionised our understanding of Titan and the potentially habitable moon of Enceladus.

However, all good things must eventually come to an end. The Cassini vehicle now has limited manoeuvring fuel left in its tanks, and while its three plutonium radioisotope thermoelectric generators (RTGs) are still capable of producing around 600 watts of electrical power, a decision was made some time ago to ensure the probe ended its mission before its tanks were dry and it was left to tumble around Saturn, where it might one day collide with one of the moons and contaminate it.

Instead, it was decided to direct the probe to into a series of orbits which would eventually see it enter the upper regions of Saturn’s atmosphere to burn up. This might seem an ignominious end for such a grand mission, but it is not without purpose.

This final plunge will not occur until September 15th, 2017, and the flyby of Titan – Cassini’s 127th –  was the first step in that final journey, turning as it did, Cassini’s path in towards Saturn as it loops around the planet from pole-to-pole. But before that fiery end comes, the vehicle will complete 22 more orbits of Saturn which will see it repeatedly  dive between the gas giant and its series of concentric rings, giving it an unprecedented science opportunity – a dive into the unknown.

“No spacecraft has ever gone through the unique region that we’ll attempt to boldly cross 22 times,” Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington said. “What we learn from Cassini’s daring final orbits will further our understanding of how giant planets, and planetary systems everywhere, form and evolve. This is truly discovery in action to the very end.”

“Based on our best models, we expect the gap to be clear of particles large enough to damage the spacecraft,” Earl Maize, Cassini project manager at JPL added. “But we’re also being cautious by using our large antenna as a shield on the first pass, as we determine whether it’s safe to expose the science instruments to that environment on future passes. Certainly there are some unknowns, but that’s one of the reasons we’re doing this kind of daring exploration at the end of the mission.”

In mid-September, Cassini will make a final, distant pass by Titan. Distant, but still close enough for the moon’s gravity to turn the craft into its rendezvous with Saturn’s cloud-tops. And when Cassini makes that final plunge on September 15th, it will send data from several instruments  until its signal is lost.

Ahead of the April 22nd Titan flyby, Cassini captured an image of Earth as seen through the ring of Saturn. Taken on April 13th, the probe was 1.4 billion kilometres (870 million miles) from Earth. when the image was taken.

Visible in the picture are, on the right, the A ring and the Keeler and Encke gaps, with the F ring over to the left. Earth is plainly visible in the gap between the rings. During this observation, Cassini was looking toward the backlit rings with the sun blocked by the disk of Saturn. The part of Earth facing toward Cassini at the time was the southern Atlantic Ocean.

Seen from Saturn, Earth and the other inner solar system planets always appear close to the sun much like Venus and Mercury do from Earth. All orbit interior to Saturn; even at maximum elongation, they never get far from the Sun. Early this month, as viewed from Saturn, Earth was near maximum elongation east of the sun, thus an “evening star,” making it an ideal time to take a picture.

Continue reading “Space Sunday: Cassini’s Grand Finale begins; Voyager’s Grand Tour remembered” →