It took Fernando Alonso just over 40 laps to complete the first stage of his Indy 500 assault today, the Rookie Orientation Procedure.

The procedure is one all rookies have to undergo and involves completing a number of laps at designated speeds.

Phase 1 involves 10 laps that must range between 205 and 210 mph. Phase 2 comprises 15 laps between 210 and 215 mph. Finally, phase 3 sees the rookie completing 15 laps at over 215 mph. Equipped with just five sets of tyres, the laps do not have to be run consecutively.

With an eye on the weather, the Indianapolis radar revealing that heavy rain was heading in, once Marco Andretti had completed a number of laps to give the Spaniard a base set-up, Alonso was sent out, the lunch break aborted in order that the F1 star might complete his running before the rain hit and the day's running brought to an end.

Over a series of runs of around 10 to 12 laps the two-time world champion was soon up to speed, encountering one minor wobble as he glided through the phases, each time setting consistent times, impressing all who were present including previous Indy 500 winners Mario Andretti and Johnny Rutherford.

"My first time in an Indy car was fun," he said following the test. "I think it was a good way to start to get the speed.

"It was a little bit difficult at the beginning to reach the minimum, but then on the next stages the car felt good. But, yeah, now hopefully we can put some laps and start feeling a little bit of the car because at the moment the car is driving itself, I am not driving the car.

"I do feel more comfortable going faster, not because of the speed, but because of the laps. You are already 30 laps in or 40 laps in, so you are able to fine tune and read the lines and up shift, down shift, learn which gear to use in which corner, etc.

"At the moment everything looks good but now we'll start the real thing. The feeling of the simulator is quite realistic and you have the first touch - the first impression of how it is going to be, but then the real car is just a unique feeling so when you have to go flat out in the corners it's not the same in the simulator that it is in the real car.

"So far, the car has been good; the team is amazingly helpful - everyone, Marco this morning, etc. Running alone I think it is quite okay, we'll see later on in the next weeks."

"He gets it," said team boss Michael Andretti. "He's one of the best in the world and you can see why. He had a little bit of understeer in that run and he adjusted his line because of the understeer. He's the real deal. I think he's going to be really strong this month."

Three generations of Andretti racers - Mario, Michael and Marco - as well as 2016 winner Alexander Rossi and 2003 winner Gil de Ferran were among those giving Alonso advice.

Marco Andretti said cooler track conditions, with ambient temperatures in the low 50s, combined with Alonso being the only driver on track provided an ideal setting for the initiation. Alonso kept churning out laps amid a threat of afternoon showers as darker clouds drifted over the speedway.

"With this level of downforce, this is like race downforce, when there's no traffic and you're by yourself, it's just stuck," said Marco Andretti. "The front and rear are stuck right now, which is what you want for the first run."

And what of sorting out the input from so many voices?

"He'll have to learn by fire from a lot of it," said Marco. "But he's asking the right questions. He'll be fine. He's a race car driver. He'll leave today pretty confident."

The Spaniard will now focus on F1 and his home Grand Prix before heading back to Indianapolis the day after for the opening practice session.

Check out our gallery, here.