"Neither of us have been to the United States before ... we're really looking forward to visiting the space centre, it's iconic," Kesia said.
The pair applied for the challenge after seeing it online.
Their project was originally done for a school science fair and investigated nitrogen-fixing bacteria, and using bacteria as fertilisers.
"Many fertilisers are not good for the environment. We developed a more sustainable alternative using bacteria," Kesia said.
Their project will be entered in the energy and environment category.
To see what other contestants had to show would be really exciting, Shulan said.
Kesia said the pair would head to the United States a week prior to the competition to visit some tourist attractions.
The girls are being supported to attend by the Talented School Students Travel Award fund administered by the Royal Society of New Zealand and funded by the Ministry of Business, Innovation and Employment.
Debbie Woodhall, project co-ordinator at the Royal Society of New Zealand, said this was the first time students have been funded to attend this particular competition.
"They have done extremely well to get this far and to represent New Zealand. They are talented high achievers."
Kesia and Shulan's project was entered into the 2016 Bay of Plenty regional science fair and won five awards.
They were mentored by CREST consultant Sarah Addison, from Scion Research.
Beccy Ganley from Scion will be accompanying the girls to the USA as their coach. The Zonta Club of Rotorua is also supporting the trip.
Shulan is in Year 13 while Kesia completed her Year 13 last year and is now studying towards conjoint engineering and science degrees at the University of Auckland.
