The US space agency, Nasa has delayed the launch of its New Horizons mission to Pluto until Thursday, following a power cut at a key operations centre.
The lift-off from Cape Canaveral in Florida was originally scheduled for Tuesday, but high winds forced Nasa to scrub that attempt.
Now a storm in Maryland, where the Johns Hopkins University control centre is based, has forced another delay.
Pluto is the only remaining planet that has never been visited by a spacecraft.
The operations centre in Maryland needs to take control of the spacecraft after separation of the second stage of the Atlas 5 rocket.
Mission guide: New Horizons
A mission to an unexplored planet is being launched for the first time since the Voyager craft left for Jupiter and Saturn in the 1970s.
New Horizons' trip to Pluto and the Kuiper Belt Objects will mean that all the Solar System's planets have been visited.
The huge distance New Horizons must cross to reach Pluto means it will not arrive until July 2015 - at the very earliest.
To achieve that, Nasa must launch the probe before 3 February, so that it can "slingshot" around Jupiter and use the planet's gravity to achieve speeds of about 25km/s (56,000mph).
Any later and it will be an unassisted flight to Pluto that could take until 2020.
Nasa considers reaching Pluto part of its "historic endeavour" of planetary exploration and New Horizons a chance to "understand worlds at the edge of our Solar System".
Pluto and its moon, Charon, form a double or binary planet - an arrangement which is thought to be common, but which has not been studied in detail before.
It will also be the first time that one of the "ice dwarf" planets and the hundreds of Kuiper Belt Objects beyond Neptune's orbit have been visited.
Click here to see New Horizons' route to Pluto
New Horizons will be launched on board a powerful Atlas V rocket from Cape Canaveral in Florida, sometime from 17 January onwards.
If the launch takes place on schedule, New Horizons will spend the first 13 months heading towards Jupiter, with key checks taking place.
For the next eight years, New Horizons will cruise towards Pluto, being "woken" annually for technical checks and rehearsals for its encounter with the planet.
Long before it approaches Pluto, New Horizons will start collecting data. The first maps of Pluto and Charon will be made three months before the period of closest approach.
During the day-long fly-by, ultraviolet emissions from Pluto's atmosphere will be measured and the best quality maps of Pluto and Charon, including surface detail, will be made.
At the closest point, New Horizons will be 10,000km (6,200 miles) from Pluto and about 27,000km (16,800 miles) from Charon.
The probe will then look back at the "dark side" of the double planet to spot haze, look for rings and examine the objects' surfaces.
Even then, the $650m (£368m) mission may not be over; with Nasa approval it will travel on to an as yet undecided Kuiper Belt Object for further studies.
The lift-off from Cape Canaveral in Florida was originally scheduled for Tuesday, but high winds forced Nasa to scrub that attempt.
Now a storm in Maryland, where the Johns Hopkins University control centre is based, has forced another delay.
Pluto is the only remaining planet that has never been visited by a spacecraft.
The operations centre in Maryland needs to take control of the spacecraft after separation of the second stage of the Atlas 5 rocket.
Mission guide: New Horizons
A mission to an unexplored planet is being launched for the first time since the Voyager craft left for Jupiter and Saturn in the 1970s.
New Horizons' trip to Pluto and the Kuiper Belt Objects will mean that all the Solar System's planets have been visited.
The huge distance New Horizons must cross to reach Pluto means it will not arrive until July 2015 - at the very earliest.
To achieve that, Nasa must launch the probe before 3 February, so that it can "slingshot" around Jupiter and use the planet's gravity to achieve speeds of about 25km/s (56,000mph).
Any later and it will be an unassisted flight to Pluto that could take until 2020.
Nasa considers reaching Pluto part of its "historic endeavour" of planetary exploration and New Horizons a chance to "understand worlds at the edge of our Solar System".
Pluto and its moon, Charon, form a double or binary planet - an arrangement which is thought to be common, but which has not been studied in detail before.
It will also be the first time that one of the "ice dwarf" planets and the hundreds of Kuiper Belt Objects beyond Neptune's orbit have been visited.
Click here to see New Horizons' route to Pluto
New Horizons will be launched on board a powerful Atlas V rocket from Cape Canaveral in Florida, sometime from 17 January onwards.
If the launch takes place on schedule, New Horizons will spend the first 13 months heading towards Jupiter, with key checks taking place.
For the next eight years, New Horizons will cruise towards Pluto, being "woken" annually for technical checks and rehearsals for its encounter with the planet.
Long before it approaches Pluto, New Horizons will start collecting data. The first maps of Pluto and Charon will be made three months before the period of closest approach.
During the day-long fly-by, ultraviolet emissions from Pluto's atmosphere will be measured and the best quality maps of Pluto and Charon, including surface detail, will be made.
At the closest point, New Horizons will be 10,000km (6,200 miles) from Pluto and about 27,000km (16,800 miles) from Charon.
The probe will then look back at the "dark side" of the double planet to spot haze, look for rings and examine the objects' surfaces.
Even then, the $650m (£368m) mission may not be over; with Nasa approval it will travel on to an as yet undecided Kuiper Belt Object for further studies.