In today’s Bulldog wrapup of technology and science news:

  • Uber says it will keep self-driving cars in San Francisco 
  • Hotel search site Trivago rises in stock market debut 
  • Hydroelectric engineers find potential in centuries-old mine
  • Galileo, Europe’s rival to GPS satnav system, starts service 
  • After harsh light, a cheaper version of EpiPen from Mylan

The details:

  • Uber says it will keep self-driving cars in San Francisco

Uber’s self-driving cars will keep ferrying passengers around San Francisco, the ride-hailing company said Friday — a few hours before state prosecutors threatened to haul Uber before a judge if the service is not suspended immediately.

In a sharply worded letter, attorneys with the California’s Department of Justice demanded that Uber get a special state permit if it wants to continue. If not, “the attorney general will seek injunctive and other appropriate relief,” according to the letter.

Though there was no deadline in the letter, a spokeswoman for California transportation regulators, Melissa Figueroa, told The Associated Press in a text that the state would take action “early next week” if Uber doesn’t comply.

Uber began the pilot project Wednesday with a few Volvo SUVs that are tricked out with a suite of sensors allowing them to steer, brake and accelerate. A person sits behind the wheel, just in case.

Officials with Uber and the state have talked several times this week after the state Department of Motor Vehicles issued a similar legal threat. The leader of the company’s self-driving program, Anthony Levandowski, described those as “frank conversations” which left him unswayed .

State lawyers insist that Uber’s cars are “autonomous vehicles” which need the permit to ply public roads.

Levandowski said he respectfully disagrees, arguing Uber does not require the permit that 20 other companies testing the technology in California have gotten because the Volvos have backup drivers behind the wheel monitoring the cars. That means the Volvos are not “autonomous vehicles” under the state’s definition, he argued.

  • Hotel search site Trivago rises in stock market debut

Shares of Trivago, the hotel search company that created a buzz with a rumpled TV spokesman, rose in their Wall Street debut.

Travelers use the German company’s websites and apps to search for hotels around the world. Trivago makes money when a user clicks on a hotel, goes to another site and books a room.

Its TV commercials have featured the same spokesman, Tim Williams, for years.

Trivago NV raised more than $287 million after it and its shareholders sold 26.1 million American depositary shares for $11 apiece. The price was below its previously-expected range of $13 to $15 ADS. The stock is trading on the Nasdaq stock exchange under the symbol “TRVG.”

The ADS rose 85 cents, or 7.7 percent, to close at $11.85 Friday.

  • Hydroelectric engineers find potential in centuries-old mine

Some look at an abandoned, centuries-old iron mine in New York’s Adirondacks and see a relic.

An ambitious group of engineers sees the shafts in Mineville as a new way to provide a steady flow of electricity in a growing market for renewable energy.

They are pitching a plan to circulate some of the millions of gallons of groundwater that have flooded the mine shafts over the years to power an array of 100 hydroelectric turbines a half-mile underground.

They envision the operation as a solution for solar and wind power producers, who need ways to ensure an uninterrupted flow of energy when the sun isn’t shining and winds are still.

“Today, everyone’s recognizing that a critical part of our energy infrastructure is going to be storage,” said Jim Besha, head of Albany Engineering Corp., as he gave officials a tour of the mine site about 100 miles north of Albany. “You can think of it as a bank. If someone has excess solar energy, they would pay a fee to store it overnight.”

While logistically complex, the plan is at the same time incredibly simple: Engineers would drain roughly half of the water from the shafts and pump the remainder into an upper chamber. The water would then be released into a lower chamber, powering turbines and creating electricity. The turbines would be reversed to pump the water back up to repeat the process.

Technically, the pumped water is considered stored energy, to be released strategically when power is needed.

The Mineville Pumped Storage Project still faces federal approvals and up to three years of construction, but it could become one of the first projects of its kind in the nation.

  • Galileo, Europe’s rival to GPS satnav system, starts service

Eight years late and billions over budget, European officials flipped the switch Thursday on a satellite navigation system meant to rival the U.S.-made GPS service that’s become a staple feature of smartphones and cars worldwide.

The Galileo system, named after the Italian engineer and astronomer, is designed to provide commercial and government customers with more precise location data than GPS.

Being able to pinpoint a position is critical to a growing range of products and systems, including real-time logistics, self-driving cars and drone delivery services.

Satellite systems such as GPS also play an important role in providing precision timing for financial transactions and energy grids.

The launch of the first 18 Galileo satellites was hit by delays and several failures. One satellite has stopped working and two others ended up in the wrong orbit.

But the European Space Agency managed to launch four satellites on a single rocket last month and expects to have a full complement of 24 satellites, plus spares, in orbit within four years.

Galileo originally was meant to begin service in 2008 at a cost of 3 billion euros ($3.1 billion), but the development and operation is now expected to cost 13 billion euros by 2020, German news agency dpa reported.

While GPS receivers are standard in millions of devices already, only a handful of gadgets support the Galileo system so far.

Galileo’s free consumer signal will provide location data offering precision within about one meter (3 feet, 3 inches), compared to 5 meters (16 feet) or more for GPS. A premium service eventually will offer even greater precision to paying customers and police, fire departments and government agencies.

  • After harsh light, a cheaper version of EpiPen from Mylan

Mylan is releasing a generic version of its emergency allergy treatment EpiPen at half the price of the much-critcized branded option.

Mylan NV said Friday that it will charge $300 for the generic version of its life-saving injections, which come in a two pack. The generic version will begin to reach retail pharmacies next week.

The list price of an EpiPen two-pack, which is stocked by schools and parents of children with severe allergies, now tops $600, an increase of more than 500 percent since 2007, when Mylan bought rights to the drug. The price hikes drew scorn and Congressional inquiry.