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Engineers test the RL-10 engine in NASA Lewis (now Glenn) Research Center's Propulsion Systems Laboratory. (credit: NASA)

NASA is making good progress on developing the core stage of its Space Launch System rocket, as directed by Congress in 2010. Per the request of legislators, the agency is using legacy hardware such as the space shuttle's main engines to propel this core stage and solid rocket boosters to give it an initial kick off the launch pad.

Meanwhile, the agency hasn't yet settled on an architecture for the upper stage of the massive rocket, which is used to boost payloads beyond low-Earth orbit and into deep space. For at least the first, uncrewed flight in 2018, NASA will use an interim upper stage. But Congress has been pressing the agency to settle on a new, permanent upper stage, dubbed the "Exploration Upper Stage," in time for the second launch of the SLS rocket in 2022 or 2023.

According to an insider website, NASASpaceflight.com, the agency had been considering nine proposals for the upper stage, but it has now chosen an architecture that uses four RL-10 engines as it moves forward. The RL-10 engine, a workhorse developed in the late 1950s and first flown in 1963, runs on liquid hydrogen/liquid oxygen fuel.

You too can look as cool as Ars' own Sebastian Anthony when trying the Vive at a retail demo station.

No matter how many reviews you read or how many videos you watch, you can't really understand what the new round of virtual reality hardware is like until you try it. For those without an early-adopting, VR-savvy friend nearby, HTC is rolling out dozens of retail demo stations where you can put the SteamVR-powered Vive through its paces. And if the demo convinces you to lay down at least $800 on a piece of the future, those retail location will also be taking pre-orders for delivery beginning in June, according to HTC.

Currently, the Vive demos are only available at three Microsoft Stores—in New York City, Bellevue, and Salt Lake City. Microsoft has plans to expand the program to 11 more stores in the US (and one in Sydney, Australia) by the end of the month and up to 30 locations by the end of the year. (Users have to be 18 years old to take part in the demos, according to Microsoft's website.) Gamestop, meanwhile, will start demonstrating the Vive at 10 locations across the US starting April 18.

That's a lot of Vive demo stations to keep track of, so we threw together a quick Google Map (below) that shows how far you'll have to travel to get your free taste of the headset (color-coded by retailer and demo start dates, click through for more details). Customers in central Florida, the New York area, Southern California, and the Pacific Northwest are spoiled for choices, while pickings are currently much slimmer in the vast middle of the country. Who's up for a really nerdy roadtrip?

Just open access to +1.1 million papers, nbd.

Most of you have probably heard of arXiv.org by now. Basically, every paper I report on is probably on the arXiv in some form. The site hosts draft manuscripts in physics and astronomy. Many of them eventually appear in academic journals, although others will spend their entire existence in the arXiv.

Five years ago, I assumed that every field had its own equivalent of arXiv. So imagine my surprise when I tried to upload my first chemistry paper to the chemistry equivalent. Apparently, there was one—but publisher Elsevier eventually gained control of it and began requiring registration. The site is probably a wasteland by now.

Until recently, biology hadn't even managed to create anything that Elsevier would want to acquire. But now, biologists are finally getting on the pre-print train with a bioRXiv.

(credit: ALFRED SACCHETTI, MD)

One man's Fitbit device proved to be much more than a smart pedometer. After a 42-year old New Jersey man suffered a seizure at work one day, emergency room doctors used his Fitbit Charge HR to understand his heart rate history and decide how they could best treat him.

Upon arrival at Our Lady of Lourdes Medical Center in Camden, doctors noticed that the man had an atrial fibrillation, or an irregular, fast heartbeat. However, they weren't sure if it was a chronic condition or if it was caused by the seizure itself. Knowing this detail would determine how the doctors could treat the patient: If the arrhythmia was caused by the seizure, they could electrically cardiovert the patient to alleviate it. If it was chronic, the cardioversion could potentially cause a stroke. A stroke could also occur if the arrhythmia was left untreated.

That's where the man's Fitbit Charge HR came in. The doctors accessed the Fitbit app on his smartphone and found his average heart rate as recorded throughout the course of his fitness program. "[It] revealed a baseline pulse rate between 70 and 80 beats/min, with an immediate persistent increase to a range of 140 to 160 bpm at the approximate time of the patient’s seizure. The pulse rate remained elevated until administration of the diltiazem in the field," researchers wrote in the report that now appears in the Annals of Emergency Medicine.

Who's that behind you? Oculus's prying eyes, that's who! (credit: Oculus)

Critical backlash against Oculus's privacy policy reached Capitol Hill on Thursday, when Sen. Al Franken (D-Minn.) demanded that Oculus and its parent company Facebook answer for the data its new headset collects from virtual reality users.

"Oculus’ creation of an immersive virtual reality experience is an exciting development," Franken wrote in an open letter to Oculus CEO Brendan Iribe, "but it remains important to understand the extent to which Oculus may be collecting Americans’ personal information, including sensitive location data, and sharing that information with third parties."

The question is, what exactly is Oculus asking to collect—and how much worse is it compared to other online services' EULAs?